The severity of hazard of a variety of cross connections depends upon the type of contaminant or potential contaminant which the public system is cross connected to, and also the likelihood of backflow. Backflow can be caused by either backsiphonage or backpressure situations. Pages 30 through 34 illustrate both backsiphonage and backpressure backflow conditions as well as some typical corrective measures to prevent backflow.

In reviewing section R 325.11403 of the water supply cross connection rules, various types of cross connections are mentioned. A brief review follows:

14.4.1 "A cross connection shall not be made between a public water supply system and a secondary water supply."

Many industrial and commercial establishments as well as some private dwellings maintain a secondary source of water in addition to the public water supply. These rules make it illegal to maintain a cross connection with any well water source which is not under the control of the water utility and any surface water supply. For the purpose of identification, privately owned and operated wells will be classified as follows:

Class I Well: Isolation and construction meet community (type I) public water supply standards with a good bacteriologic record.

Class II Well: Isolation and construction meet type IIb or type III public water supply standards with a good bacteriologic record.

Class III Well: Isolation, construction, and/or bacteriologic records not acceptable or not ascertainable.

In addition, many industries and commercial establishments have made an effort recently to conserve on water use and have utilized cooling towers and recirculation systems for this purpose. Due to the design and normal operation of these cooling towers, it is very possible that the water being recirculated to the inplant system is contaminated chemically and/or bacterially. Therefore, these recirculated water systems are considered secondary supplies.

Where there is a secondary water source, it is extremely important that the users' systems be carefully inspected to make certain that none of the protective devices installed are bypassed. In reviewing the plant piping, it is recommended that a determination be made as to the location of the most critical pieces of equipment present in the plant; those requiring a continuous supply of water. Equipment such as furnaces, compressor units, and some boilers may be in the critical equipment category and as such will be the location where direct cross connections will likely be found. Inspections and reinspections of inplant facilities must include review of these areas of primary concern.

BACKFLOW DUE TO BACKSIPHONAGE

Fire systems in industries with secondary water supplies must be carefully reviewed to determine whether or not the two systems have been cross connected. If some consideration is being given to the installation of protective equipment, such as reduced pressure principle backflow preventers, the system must be designed to utilize the water at a reduced pressure. If the fire system cannot operate satisfactorily at a reduced pressure, an alternate design must receive consideration.

Horizontal centrifugal pumps are often used to distribute a secondary water supply to the internal piping system. Particularly when a surface water is used, attention must be given to the water source used to prime the pumps. This is often a direct connection between the public supply and the secondary supply. Pumps for auxiliary systems, cooling systems, and fire systems must be considered as points requiring inspection. Also, pumps which recirculate water from cooling towers or substandard storage facilities must be inspected.

When a storage tank forms an integral part of an industrial or other system, it may be necessary to consider it a source of secondary supply. This will be the case with appropriate protection required if the storage facilities do not meet construction standards for drinking water or if the stored water is treated in any way.

14.4.2 "A cross connection shall not be made by submerged inlet."

Submerged inlets are serious potential hazards on public water supply distribution systems. Plating tanks, wash and rinse tanks, and similar installations in industrial establishments must be considered potential sources of contamination since chemicals such as chromium, nickel, and cyanide are in use routinely. In some instances, management has cooperated with requests that water lines submerged in individual plating tanks be removed. Air gaps were installed satisfactorily only to find upon reinspection that the water lines had generally been restored to a submerged condition. This replumbing job was often done without the knowledge of management personnel. The workers simply replaced the submerged inlets to avoid splashing or to provide for better mixing of the chemicals in the tank. Therefore, an air gap at individual plating tanks cannot be considered to be reliable protection against the possibility of cross connections. Vacuum breakers have been used to protect internal piping systems by being installed at such locations as plating tanks, rinse tanks, medical, pathology, or research (bacteriological and/or chemical) laboratory sinks, mortuary tables, etc. Historically, many of these devices have been removed or altered in such a manner, due to minor problems such as the devices leaking or spitting, that the protection for the internal piping system is voided. Therefore, a second line of defense in addition to vacuum breakers must be provided on the public service line to the building or potable water line to the area of concern, particularly with those customers where multiple submerged inlets may be created or where reinspection may be cumbersome.

Submerged inlets can often be found in plating plants, hospitals, medical laboratories, nursing homes, mortuaries, and photo laboratories. It is apparent that many of the potential contaminants could be of a variety which would not discolor the water and quite possibly would not be noticed until sickness or death occurred.

The internal piping systems of hospitals, nursing homes, and homes for the aged are inspected annually as part of an ongoing licensing program carried out by the Division of Health Facility Licensing and Certification, Bureau of Health Care Administration, Michigan Department of Public Health. It will be satisfactory for the local inspection agency, as a part of their program, to accept the annual license as evidence that the interior piping system is acceptable. However, because of the hazardous types of cross connections which are involved in hospitals, it is required that the service line from the public distribution system be protected at the point where it enters the hospital building(s) by either an approved air gap or a reduced pressure principle backflow preventer. If desired, the local inspection agency may also inspect the interior piping system. If a reduced pressure principle backflow preventer is installed on the service line, it does not relieve the need for a high degree of protection throughout the internal piping system. This is of particular importance considering the function of hospitals.

The plan submitted to the Michigan Department of Public Health by the local water utility should clearly outline the procedure to be followed in these instances. The plumbing inspection agencies in some communities may carry out strict enforcement programs within hospitals. This is certainly a desirable and commendable program and is encouraged.

14.4.3 '1A cross connection shall not be made between a public water supply and piping which may contain sanitary waste or a chemical contaminant."

This type of situation would be encountered where: a pipe or tank containing potable water is discharged to a sanitary sewer and could be subject to backflow; when the public system is connected directly to an industrial or commercial establishment where some chemical additives have been applied to the water supply and are of a concern to the potability of the water. Boilers and steam systems would be included in this subject area. Fire fighting systems in some instances contain water treated with an anti-freeze chemical to prevent freezing. Certainly, toxic chemicals such as ethylene glycol (automobile anti-freeze) shall NOT be used in this manner, but often times complete control is lost over the use of such chemicals. Propylene glycol is an example of a chemical which is non-toxic and can be used as an anti-freeze protection; however, it, too, must be maintained separate from the public system and the potable supply. Whenever a chemical is proposed for this purpose, it is suggested that the water utility or inspection agency provide all pertinent data relative to its chemical make-up to the Michigan Department of Public Health for a determination of its toxicity prior to allowing its use.

The incident at Holy Cross University in 1969 illustrates the seriousness of not properly protecting the public system from backsiphonage backflow from lawn irrigation systems. Protection devices must be properly selected and installed to prevent this from happening, and some consideration should be given to local permit systems to control lawn sprinkling installations, etc.

Refrigeration systems are potential sources of contamination due to the chemicals generally used in the process. Therefore, supermarkets, etc., must be monitored relative to the possibility of cross connections.

Marine vessel watering points located along the Great Lakes shoreline should be separated from the public water supply system by properly installed reduced pressure principle backflow preventers. The water supply in marinas for pleasure craft must be protected to prohibit backflow. In marinas where the supply is subject to both backpressure and backsiphonage, a reduced pressure principle backflow preventer should be installed. Where backsiphonage only is possible, a properly designed vacuum breaker system may be acceptable.

14.4.4 "A cross connection shall not be made between a public water supply system and piping immersed in a tank or vessel which may contain contaminants."

Water is often used as either a coolant or a source of heat in certain chemical processes. This usually requires submerging water piping in various contaminants. Since the piping is subject to corrosion and leakage, the result is a submerged inlet depending upon the condition of the piping. Commercial laundries and associated heat reclamation facilities are another source of concern for this type of cross connection. (See Section 14.4.5.3 on Common Wall Heat Exchangers.)

14.4.5 Specific Hazards

The following are discussions about specific cross connection hazards a water utility may encounter.

14.4.5.1 Booster Pumps

Booster pump installations should be reviewed by the local water utility and should not be allowed at locations where there is not a satisfactory supply of water with a minimum residual pressure of 20 psi. Booster pumps may be installed only in cases where additional pressure is desired and not in any instance where additional quantities of water are required. Low pressure problems should be solved by installation of larger service lines, improving the distribution system in the area, or adding source capacity as necessary to meet system demands.

14.4.5.1.1 Domestic booster pumps

If booster pumps are required for domestic piping in high-rise buildings, the preferred solution is the installation of a storage tank supplied from the public system through an acceptable air gap with repumping to the user's system. In some instances, an in-line booster pump may already be in service. The inspecting agency must make certain that at the very least a low pressure cut-off switch or equivalent is installed to stop the pump if the pressure at the pump suction drops to 20 psi.(1)

Another means that may be employed to maintain positive suction pressure on a booster pump is that of a pressure sustaining control valve installed on the booster pump discharge piping. Controls for such a valve may be preset to a specified minimum suction pressure to throttle the control valve as minimum suction pressures are approached. One of the advantages of this control measure is that flow from the booster pump is maintained, though at a lower rate, rather than a no flow condition which occurs with a low pressure cut-off switch arrangement.

14.4.5.1.2 Fire booster pumps

The installation of high capacity fire pumps cannot be tolerated at a point where the distribution system is inadequate or on a system where the total water source is insufficient. This would be particularly critical in many of the smaller communities in Michigan where the source may not be capable of meeting the high, point (fire) demands which might be placed on the system. This restriction must also apply to high capacity fire department pumper trucks.

The following guidelines should be referenced when evaluating fire booster pumping installations:

1. Unless there is evidence of low pressures at the required demand rates in the vicinity where a fire booster pump installation exists, it will not be necessary to require the installation of a low pressure cut-off switch or other device necessary to control the suction pressure on the fire booster pump. The need for installation of a backflow prevention device must be evaluated independently.

2. The water utility should periodically evaluate its system's fire fighting capability from a flow and pressure standpoint in those areas where fire booster pumps are incorporated.

(1) Minimum suction pressures allowable may vary depending on conditions in the area such as presence of high-rise buildings, peak flow capabilities, system demands, etc.

3. In those instances where an existing fire booster pump installation is located in an area of marginal flow and residual system pressure, a pressure sustaining control valve or low pressure cut-off to control the pump suction pressure should be installed. Again, the pressure sustaining control valve is the preferred choice. An area of marginal system pressures may be defined as that area of a water distribution system where flow at a residual pressure of 20 psi is less than 1.25 times the sum of the rated capacity of the booster pump and the known or estimated maximum day demand of the area EQ < 1.25 x (Cap. of B.P. + Max. Day of Area)].

With regard to water supply systems that may experience marginal fire flows and residual system pressures, fire department personnel should be made aware of the areas where pressures are low during peak use periods. Fire pumpers must not be allowed to draft directly from hydrants which are located in areas of marginal system flows.

Fire pumper trucks frequently carry a volume of water in the event little or no municipal water is available at the point of need. Whenever a connection is made from one of these pumpers to a municipal system, the potential exists for backflow, especially if other pumpers are also drafting water in the vicinity. Water utilities and fire departments should strive to assure that, whenever possible, the source of water hauled in the fire pumpers or tanker trucks is from an approved source of supply and that the storage tank is periodically disinfected.

14.4.5.2 Chemical Treatment of Customer Piping Systems

Water utility managers may not be fully aware of all chemicals being added to water supplies on customer premises until a cross connection inspection program has been completed. Under Michigan's cross connection control rules, the water utility is responsible for protecting against cross connections which might contribute to the contamination of the public drinking water supply either through backsiphonage or backpressure backflow.

There are many forms of cross connections and varying degrees of hazard associated with them. This discussion is limited to cross connections associated with chemical additives that are relatively innocuous, such as polyphosphates and propylene glycol. Though these types of chemicals are non-toxic, the water utility manager must be concerned about how they are added to or controlled in the customer's water distribution system.

The key to drinking water safety is control -- control over connections to the system, control over what the customer feeds into the system, control over how the customer uses water from the system, and control over changes that may be made to utility-approved customer actions.

Water utilities should be capable of providing a quality of water that can be used without further treatment. In some instances, this is not always possible, and the customer may desire to alter the water's chemical characteristics. As the Michigan Department of Public Health is required by statute to approve, regulate, and supervise water treatment plants, the water utility is responsible by the cross connection rules to approve, supervise, and control treatment and uses by the customer. In carrying out these responsibilities, a water utility should establish specific procedures.

Where toxic substances are involved, the positive protection afforded by an air gap or a reduced pressure principle backflow preventer may be required on the customer service. When it is determined that this kind of protection is necessary for the public water supply, the customer should be advised of the potential hazards to those drinking the water within the customer's establishment. When non-toxic substances are proposed to be added by a customer, other means of backflow prevention, following close review, may be allowed. However, it is the responsibility of the utility to determine the degree of protection necessary. The following should be considered when making the decision as to what minimum protection should be provided:

Is the chemical necessary?

Will it accomplish the desired end result?

Is the chemical approved for addition to water supplies by the Michigan Department of Public Health and at what dosage rates?

Type of positive displacement feed equipment proposed (The Michigan Department of Public Health does not approve venturi or siphon feed equipment.)

Location of chemical feed point.

Means of controlling feed system (licensed operators vs. inexperienced personnel in attendance).

Control methods (paced vs. unpaced chemical feed).

Frequency of utility cross connection reinspection.

Likelihood of the customer changing the chemical feed without notice to the water utility.

14.4.5.3 Common Wall Heat Exchangers

History has shown repeatedly that the wall structure of a common wall heat exchanger separating a potable water system from the heat exchange medium can fail thereby creating an avenue for contaminants to enter the potable water supply system. Common or single wall heat exchangers have existed for many years and continue to pose a potential health problem when they are used as a means to heat potable water systems, such as those in schools or hospitals, that may be utilizing chemically treated steam or hot water boiler systems. Some of the solar energy systems being marketed today for supplementing heat to potable hot water systems also incorporate a common wall heat exchanger. These, like the steam and hot water boiler heat exchangers, pose a threat to public health, particularly in cold climate regions where anti-freeze solutions may accompany corrosion inhibitors in the exchange medium.

Water utilities can assure protection of the municipal water supply from this application of the heat exchanger typically in one of three ways. One method is to call for service line protection for those customers who may utilize a single wall heat exchanger. This method assures complete protection for the utility, but does not provide any protection whatsoever for the building occupants. Another means is to assure through periodic inspection that non-toxic additives are being safely added to the building piping system. This approach is preferred over service line protection in that both the water utility and building occupants are afforded protection. When feasible, this approach should be followed. The water utility and building owner who utilizes boiler chemical treatment must both assume responsibility for assuring proper maintenance and control of the treated piping system. A third method that may be utilized to protect the municipal system as well as building occupants is to require replacement of the single wall heat exchanger with a double wall or a double heat exchanger installation.

Other types of heat exchangers may be encountered which utilize potable water as the heat exchange medium or coolant. Many of these are associated with certain types of refrigeration systems or engine cooling system. Depending on the nature of possible contaminants involved and the design of the overall heat exchanger, full protection on the potable water service to such units may be necessary.

From a design standpoint, the following criteria have been established in conjunction with the Division of Plumbing, Department of Labor, to protect a potable hot water system against contamination from a heat transfer fluid:

Heat exchangers shall be divided into 3 basic types:

Type Type of Separation

NW None

SW 1] Single Wall

DWP 2] Double Wall (two wall)

1] Single Wall: Based on a review of pertinent operational data, additional design criteria may be required for specific installations by the local plumbing official.

2] Double Wall (Two Wall): This shall mean two separate walls with a leak path (void) between the walls that is open and drainable to the atmosphere so as to provide telltale evidence of leakage in either wall.

Installations consisting of tubing or a plate coil wrapped around, and bonded to, a tank will be considered as having double wall (two wall) separation if the distance between the bonded areas on the tubing or plate coils are equal to, or greater than, the width of the bonded area.

Double heat exchangers (three stage heat exchangers) with potable intermediate transfer fluid vented to the atmosphere shall be considered equivalent to double wall separation.

Heat transfer fluids shall be divided into 3 basic classes:

Class Heat Transfer Fluid

Class I Potable

Class II 1] Essentially Non-toxic

Class III 2] Essentially Toxic

I] Class II heat transfer fluids are typically materials with a Gosselin toxicity rating of 1, which are neither mutagenic, teratogenic, or carcinogenic to humans or laboratory animals, and which are known not to bioaccumulate in humans or laboratory animals. Examples of fluids which typically might fall in Class II are: Propylene glycol, mineral oil (USP), glycerin (USP), polydimethysiloxane, freon, FDA approved boiler water additives for steam boilers.

2] Class III heat transfer fluids are typically materials with a Gosselin rating of 2 or 3. Examples of fluids which might fall in Class III are:

Ethylene glycol, hydrocarbon oils, ammonia refrigerants, hydrazine.

The class of heat transfer fluid that may be used with various types of heat exchangers is as follows:

Class of Heat Transfer Fluid Type of Heat Exchanger

I NW, SW, DWP

II SW, DWP

III DWP

Materials which have a Gosselin toxicity rating greater than 3 shall not be used. All additives, corrosion inhibitors, and residuals shall also be considered with the major component when classifying a fluid.

The properties of all heat transfer fluids are to be determined by an independent testing laboratory. The final classification, based on the review of pertinent test data, shall be established by the Michigan Department of Public Health.

Prior to approval and acceptance of the system, a notarized statement listing the class and name of the heat transfer fluid introduced into the system shall be provided by the owner, owner representative, or installing contractor to the plumbing official.

A permanently affixed label shall be provided at a prominent place in the system, stating:

Heat Exchanger Type _______________ (fill in)

Heat Transfer Fluid Class __________ (fill in)

WARNING: DO NOT ADD ANY OTHER FLUID TO THIS SYSTEM OR CHANGE HEAT TRANSFER FLUID TO A HIGHER CLASS. UNAUTHORIZED ALTERATIONS TO THIS SYSTEM COULD JEOPARDIZE WATER QUALITY AND POSE A SERIOUS PUBLIC HEALTH THREAT.

The above information and warning shall also be clearly noted in the owner's operating manual.

Whenever a direct make-up line exists into the chemically treated piping system, such as a make-up line into a boiler, full protection on this line is required.

14.4.5.4 Funeral Homes

A large number of funeral homes have been found to have direct cross connections via piping arrangements located in the preparatory room. All funeral homes which are served by the municipal water supply system should be given high priority when scheduling initial inspections. The cross connection usually observed within the preparatory room is typically a submerged or potentially submerged inlet. It is common to find an aspirator and/or rinse hoses attached to a sink faucet which has no protection against backsiphonage of waste. Protection of the municipal water supply system against possible contamination caused by backsiphonage can be accomplished by installing a reduced pressure principle backflow preventer on the water service line to the funeral home or on the water line(s) to the preparatory room, or by installing properly located and approved vacuum breakers in the preparatory room. If a vacuum breaker is to be utilized to protect against backsiphonage of waste from the preparatory room, it must be located above the highest point where waste may originate. When an atmospheric vacuum breaker is to be utilized on the water service line to which an aspirator or rinse hoses could be attached, it must be installed near the ceiling of the preparatory room and on the discharge side of the shutoff valves. Installation of a vacuum breaker (atmospheric or pressure type) near the ceiling is deemed necessary due to the type of instrument and technique used during the embalming process.

Personnel responsible for the local cross connection control program should also look for the lawn irrigation and boiler type cross connection at funeral homes. Corrective measures indicated in this manual should be followed to protect municipal water supply systems from contamination through these types of cross connections.

The immediate attention of cross connection inspection personnel must be given to this potential problem to assure that funeral homes are inspected for the presence of cross connections and that, when found, corrective action is taken to eliminate their presence. Health department personnel have contacted representatives from the Department of Licensing and Regulation and have received their cooperation in notifying funeral home management personnel during their licensing procedure of any potential cross connection conditions.

14.4.5.5 Marinas

Marinas often times pose a real threat to public health through the hazards of cross connections in that many existing facilities typically have unprotected hose outlets serving the individual boat slips. Also, sewage pumpout stations may pose a threat in that potable water outlets used for rinsing purposes are usually provided. In some instances, direct cross connections with a potable water supply may be used for priming sewage pumps. Due to these piping arrangements, marinas must receive high priority from the standpoint of cross connection control. As a minimum, all slip water supply outlets should be provided with a hose bibb vacuum breaker. Because of the possibility of backpressure and backsiphonage backflow occurring at some potable water use points, such as the sewage cleanout areas, full protection of the service line by a reduced pressure principle backflow preventer likely will be warranted. Utilities are again encouraged to check with the Michigan Department of Public Health should questions arise concerning acceptable means of protection.

14.4.5.6 Municipal Water Supply Distribution System

14.4.5.6.1 Stop-and-Waste Valves; Hydrant Weep Holes; Frost Proof Yard Hydrants

Many water utilities routinely use stop-and-waste valves on curb stops and weep holes on fire hydrants. These are potential submerged inlets which have been installed by the utility as an integral part of the system. No further use should be made of buried stop-and-waste valves, and the operating policy should be to replace those which are now in service on the system. When the curb stop is turned off or closed and there is no pressure on the service line, surface water can enter the individual services through the open stop-and-waste valve. When the curb stop is opened and the service again is in use, the contaminated water is forced into the building plumbing system.

Weep holes on fire hydrants are not as serious since any contaminants gaining entrance to the hydrants would tend to be discharged entirely out of the potable system when the hydrant valve is open. Hydrant weep holes are undesirable because unsatisfactory water is separated from the distribution system only by a closed hydrant valve, and at times the hydrants are used for potable water sources. Weep holes should be plugged on hydrants located in areas of seasonal high groundwater.

Frost proof yard hydrants many times operate similarly to a dry barrel type fire hydrant. As such, serious contamination can result, particularly in areas of seasonal high groundwater. Reference should be made to the appendix for a list of code approved frost proof yard hydrants.

14.4.5.6.2 Sewer flushing lines

Many older communities have connections between the municipal water distribution system and sanitary sewers in areas of the community where low sewage flow or sewers without sufficient slope exist. These connections, used for sewer flushing purposes, many times result in a very serious direct cross connection by submerged inlet. Water utilities when faced with such situations should proceed to eliminate this problem as soon as possible by incorporating proper corrective measures.

14.4.5.6.3 Fire hydrant additives

A number of northern area water utilities have been known to add chemical solutions to their fire hydrants for freeze protection. These compounds have included ethylene glycol, fuel oil, calcium chloride, and wood alcohol, each of which are unacceptable from a public health standpoint. Water utilities should strive to repair leaking hydrant valves where needed and/or pump out hydrants located in areas of high groundwater where the weep hole has been plugged. If additives must be used, only those approved by the Michigan Department of Public Health should be incorporated.

14.4.5.7 Storage Tanks

The water utility or local inspection agency should review all privately owned storage tanks to which the public water supply is connected. If storage facilities do not meet accepted standards for potable water usage, water within the private storage tanks should be considered a secondary water supply and thus be adequately separated from the public system. Plans and specifications for all future privately owned storage tanks supplied directly by the city water system should be submitted to the Michigan Department of Public Health for review and approval prior to construction.

Important public health design features to be reviewed for all storage tanks are as follows:

1. Openings; overlapping covers for hatches with locking mechanisms.

2. Vents, overflows, etc.; screened, properly constructed.

3. Ability to drain (not directly connected to sewer).

4. Disinfection procedure.

5. Internal painting system (toxicity?).

6. Treatment of water (anti-freeze, corrosion inhibitors, etc.).

7. Heating scheme (if used for wintertime operation, heat coil from chemically treated boiler?).

14.4.5.8 Fire Protection Systems

Like other situations encountered in cross connection control, the degree of backflow protection necessary for a particular fire protection system will depend on specific conditions present. Generally, it is recommended that the potable water supply be protected as outlined in AWWA Manual M-14 when serving fire systems (see appendix). Guidelines set forth in Section 14.4.5.1.2 of this manual pertaining to fire booster pumps should also be noted.

One exception to the AWWA guidelines is that the Michigan Department of Public Health will recognize the use of alarm checks (see Page 47 for illustrations), single checks, or detector check meters for certain limited installations as noted below:

Fire protection piping systems serving buildings not greater than three stories with no auxiliary source of water supply and no chemical additives utilized.

Again, the local utility could require more or less protection depending on the particular circumstance.

Fire sprinkler systems which are charged with a non-toxic anti-freeze solution (i.e., propylene glycol, etc.) should be isolated from the potable water supply by a double check valve assembly or equivalent protection.

14.4.5.9 Water Softeners

Typical water softener installations many times pose a public health threat mainly due to the waste discharge piping being terminated in a floor drain or sewage piping system thereby creating a submerged inlet cross connection. This type of cross connection can easily be eliminated by air gapping the waste drain piping from the softener above the floor drain. When discharging into a drain piping system, an air gap arrangement can be made utilizing a funnel and trap piping setup. Depending on local plumbing codes and building housekeeping, full protection from the entire softener system may be warranted. Water utilities should evaluate each installation independently and require more positive backflow protection when deemed necessary.

14.4.5.10 Residential Cross Connections

The following residential facilities and/or water use equipment historically have been shown to pose a serious public health threat through backflow from a cross connection. Some of these areas already have been outlined in the manual but are repeated here since they also relate to the residential user.

Problem Minimum Protection Required*

Private wells RPZ device or safe air gap (SAG)

Water softeners See Section 14.4.5.9

Toilet ball cock assemblies Code approved antisiphon device

Lawn sprinkler systems RPZ or approved vacuum breaker (AVB)

Hose aspirators AVB

Dry/liquid fertilizer feed AVB

Swimming pools RPZ device, SAG, or AVB

Solar installations See Section 14.4.5.3

Hose outlets, laundry tubs AVB

Use of anti-freeze or other RPZ device or SAG**

chemical additives

Given the lack of manpower and time needed to inspect all residential water users, the water utilities best approach to eliminating general residential cross connection problems may well be the public's self-awareness of the potential hazards involved.

*Care must be taken to use the proper device and to not violate any of the basic principles of application for the devices.

**Use of a non-toxic chemical additive may also be necessary to assure proper protection.

14.4.5.11 Commercial Car Washes

Many incidents of backflow from car washes over the years have resulted in contamination of municipal distribution systems. In most cases, backpressure backflow was created. As a result of these episodes, containment of the service line by a reduced pressure zone device will likely be necessary to prevent backflow. Water utilities must assure these customer facilities receive highest priority from an inspection standpoint.