Cross-connection Control and Backflow Prevention

What is a Cross-Connection?

Customers use water for many different purposes, and the water may come in contact with other substances not fit for consumption. This connection between clean water and other substances is called a “cross-connection.”

How could the water in the customers’ plumbing system flow back into the public water supply?

MPW may have to shut off a water main in isolated areas to make repairs. This may cause a drop in water pressure, allowing water inside a customer’s plumbing to flow back into the public water system due to gravity. Sometimes customers will have pumps downstream from the water meter which could inadvertently pump water back into the public water system. These are just two examples of “backflow”.

How can backflow be prevented?

Backflow can be prevented by installing a backflow preventer. This a device that is installed on a water service that will only allow water to travel in one direction—from the public water supply to the customer.

MPW's Backflow/Cross-Connection Control Program

Mount Pleasant Waterworks initiated a Cross-Connection Control Program In accordance with regulations from the South Carolina Department of Health and Environmental Control (SCDHEC). The program was initiated to safeguard public drinking water supply by preventing the water in a customer’s plumbing system from flowing back into the public water supply. The Commission requires all irrigation systems be fitted with a reduced pressure (RP) backflow prevention device (see diagram below). In addition:

• MPW inspects all businesses that sign up for service to determine if the installation of a backflow device will be required and if so, ensure that a secure, sufficient device is installed.
• MPW installs dual-check backflow devices (non testable) on all residential home meters. [MPW has retro-fitted all residential meters installed before 1987 with dual-check backflow devices.]
• MPW requires all customer with irrigation systems or fire sprinkler systems to install a Reduced Pressure (RP) backflow device (testable).
• MPW maintains records on all testable backflow devices to ensure they are tested annually and repaired when required.
  

What to look for —and how to fix— potential areas around your home that could be the source of cross-connections:

POTENTIAL PROBLEM: water hose that is attached to fertilizer, pesticide or herbicide sprayers could contaminate your water supply You can reduce the risk of contamination through this type of cross-connection by shutting off the water supply to the hose at the faucet when you are finished. Even if the hose has a valve on the nozzle attachment, any decrease in water pressure could siphon the water from the hose — or the sprayer — back into your plumbing system.

FIX: Purchase a hose bib vacuum breaker, available from any hardware store, that will prevent back-siphonage.

POTENTIAL PROBLEM: A hose left in a bucket used for cleaning.

FIX: Remove the hose from the bucket (or sink) and shut off the water at the tap.

Underground irrigation systems are one of the types of cross connections posing a health hazard to the public drinking water system. Contamination from herbicides, pesticides and animal droppings can enter your irrigation system when below ground sprinkler heads are used.

FIX: Installation of a reduced pressure (RP) backflow prevention device (example below). (Note: The Commission requires all irrigation systems be fitted with an RP device to prevent contaminated water from flowing back into the public water supply.) For more information about MPW's backflow prevention requirements concerning irrigaion systems, go to Irrigation FYI.