Private Cisterns: an Often Overlooked Potential Cross Connection
Colorado’s majestic mountains, plateaus, gorges and canyons, rolling plains and high deserts are a beauty to behold all year round and also truly awe inspiring! However, Colorado’s varied geography also makes it a distinct state with numerous remote water systems that present unique situations. One of these is the use of private water cisterns at homes to store or supplement the water supplied by a public water system. Historically, the construction details of these cisterns were not always well documented by the public water system. In addition, private cisterns have not typically been thoroughly inspected to ensure they contain robust protections of potable water. As a result, these cisterns can pose a risk to public health from backflow and may or may not be a cross connection, depending on how they are constructed and maintained.
For example, in September 2018, a consecutive water system in Delta County had total coliform (TC) and repeat TC positive samples in the distribution system. The responsible operator’s investigation identified that the distribution system was contaminated by a backflow event from a private cistern that was inadequately controlled. The cistern was tested for bacteriological contamination and came back positive for total coliform. The investigation found that the existing residential cistern was plumbed from the meter pit through a single non-testable check valve to a dole valve then to the cistern below water level. The customer service line was then plumbed to a tee between the dole valve and the cistern.
To address this unique situation in Colorado, the department has created a guidance document to provide answers to frequently asked questions about backflow prevention and cross connection control (BPCCC) of cisterns that are used by customers of public water systems.
The cistern guidance explains and clarifies BPCCC expectations for suppliers with private cisterns connected to their system. The department expects that cisterns are constructed in accordance with the Colorado Plumbing Code or be properly protected with an assembly (RPZ or testable double check) or method (air gap) as described in the guidance. The guidance and additional BPCCC documents can be found on the department’s BPCCC website.
Suppliers first need to determine whether or not a private cistern is a cross connection. If a private cistern is constructed per the 2018 Colorado Plumbing Code, it is not considered a cross-connection. In that case, the supplier only needs to keep that determination on file but does not need to track the private cistern in their BPCCC program. If the private cistern is not constructed per the plumbing code, then the cistern is a cross connection. The supplier must begin tracking the private cistern in their BPCCC program and control the cross connection within 120 days (or department approved alternative schedule) of discovery.
Does your system have private cisterns? Please review the reference guidance and if there are any questions feel free to reach out to the field services section at cdphe_wqcd_fss_questions@state.co.us.
➽ Monique Morey, PE, field services section
