What is backflow?
Cross-connection is defined as a physical connection between drinkable water and a liquid or gas that could make the water unsafe to drink. Wherever there is a cross-connection, there is a potential threat to public health from the liquid or gas contaminants.
Backflow is defined as water flowing opposite to its intended direction, either from a loss of pressure in the supply lines or an increase in pressure on the customer’s side. In either of these situations, if any affected customer’s pipes include a cross-connection, contaminants could be drawn through the cross-connection into that customer’s pipes; and, if the backflow continues, perhaps even into the water mains.
In 1974, Congress passed the Safe Drinking Water Act (SDWA), which makes public water systems responsible for keeping their drinking water safe. Because backflow through a cross-connection can contaminate the public supply, water systems require backflow preventers wherever that risk exists. These devices use valves to keep water flowing in only one direction, so a drop in pressure can't pull contaminants back into the main water lines.
In Texas, the Texas Commission on Environmental Quality (TCEQ) is charged with making sure local water providers stay compliant with the SDWA, including the rules for cross-connection control and backflow testing.
Backflow incidents do occur.
- In 2016, a backflow incident in Corpus Christi made international news. Hydrochloric acid and other chemicals were released into the water supply due to a faulty backflow preventer at an asphalt plant. This led to a no-use notice. Most of us are familiar with a boil notice, but in this case, boiling the water wasn't enough. You couldn't even shower with it because of the chemicals present.
- In 2015, also in Corpus Christi, a faulty backflow preventer on an irrigation system led to a backflow incident involving E. coli entering the city water supply.
- More Case Studies of Backflow Incidents
