A cross-connection is a connection between the drinking water system and a potential pollutant. A cross-connection can be a hose with sprayer containing fertilizer, an irrigation system, a hose in a bucket or a variety of household appliances that connect directly to the water system.
Water flows from a faucet, shower head or sprinkler system because of pressure. In the event of a main break, hydrant flush or fire fighting activity, these pressures can drop. If pressures drop low enough, the water distribution system can literally pull water out of surrounding sprinkler systems, homes or businesses. When this happens, water flows backward and is called backflow.
The water flowing back into the water system may now carry fertilizers, herbicides, pesticides, insecticides, industrial chemicals, bacteria, detergents or other hazards. Anytime you or a neighbor uses a hose to apply fertilizer to the lawn, allows water to puddle around a sprinkler head or leaves a hose in a bucket, there is a potential to pull hazards into the drinking water system.