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 use a hose to apply fertilizer to the lawn, allow water to puddle around a sprinkler head, or leave a hose in a bucket, there is a potential to pull hazards into the drinking water system.