Backflow Prevention in a Mixed-Use Building
A mixed-use building has a commercial kitchen on the ground floor, a dental office on the second floor, and apartments on the third and fourth floors. The water supply is from a municipal main at 70 psi. The building has a 2-inch domestic water service with a reduced pressure zone (RPZ) backflow preventer at the service entrance. The RPZ was installed 15 years ago and has not been tested annually as required by code. The building also has a fire sprinkler system with a 4-inch dedicated service that has a double check valve assembly (DCVA) backflow preventer. The dental office has a vacuum-assisted waste system and a sterilizer that uses water. The commercial kitchen has a dishwashing machine with a direct connection to the water supply and a grease interceptor. The apartments have standard fixtures. The local code requires annual testing of all backflow preventers and mandates RPZ for any premises with a health hazard. The building owner recently received a notice from the water authority to test the backflow preventers. The owner claims that the RPZ is not necessary because the building is primarily residential and the commercial spaces are small. He also argues that the DCVA on the fire line is sufficient for the whole building.
1. Determine the backflow prevention requirements for this building and evaluate the owner's claims.
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The building has multiple hazards. The dental office uses water for sterilizers and vacuum systems, which can create a health hazard if backflow occurs due to cross-connections. The commercial kitchen has a dishwashing machine directly connected to the water supply, which is a health hazard if there is a cross-connection with the grease interceptor or other waste. The fire sprinkler system is typically a non-health hazard unless antifreeze or other chemicals are added. The code requires an RPZ for health hazards. The existing RPZ at the domestic service is appropriate for the domestic supply, but it must be tested annually. The owner's claim that the RPZ is unnecessary because the building is primarily residential is incorrect; the presence of dental and kitchen hazards requires an RPZ for the domestic supply. The DCVA on the fire line protects the municipal supply from fire system backflow, but it does not protect the domestic supply from backflow within the building. The domestic and fire systems are separate services, so each must have its own backflow preventer. The RPZ must be tested annually, and the DCVA also requires annual testing. The owner must comply with the testing requirement. Additionally, the dental office may require a separate backflow preventer for the sterilizer if it is a health hazard, but the building RPZ provides protection for the entire domestic system. The owner should also ensure that the RPZ is installed with proper drainage and that it is accessible for testing. The consequence of non-compliance is potential contamination of the municipal water supply and legal penalties.
2. What type of backflow prevention is required for the dental office's sterilizer and the kitchen's dishwashing machine, and how should they be installed?
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For the dental sterilizer, if it is directly connected to the water supply and uses a vacuum system, it may create a health hazard. The code typically requires an air gap or a reduced pressure principle backflow preventer (RPZ) for such connections. However, if the sterilizer is equipped with an internal backflow preventer (e.g., a vacuum breaker), that may be acceptable. For the dishwashing machine, many codes require an air gap or a backflow preventer if the machine has a direct connection to the water supply and a drain that could back up. A common requirement is an air gap on the drain line and a vacuum breaker on the water supply. The installation should follow the manufacturer's instructions and the local code. For the sterilizer, an RPZ may be required if the hazard is health-related. The RPZ must be installed with a drain for relief discharge and be testable. For the dishwasher, a hose bib vacuum breaker or an air gap is often used. The contractor should verify with the AHJ. The key is that these fixtures are in a commercial setting and may require isolation from the potable water system. The owner should also ensure that the grease interceptor is properly maintained and that there is no cross-connection between the potable water and the waste system.