A cross connection is an unprotected direct (or potential) connection between drinking water piping and a contamination source. This can be as simple as a garden hose that is submerged in a swimming pool, a bucket of detergent, or other contaminated water. Other examples are supply lines connected to boilers, process equipment, or bottom-fed tanks. Under certain conditions, cross connections can allow tainted water to flow backward through the piping system and contaminate drinking water.
These unprotected cross connections are prohibited. The Wisconsin Rural Water Association has made available a brochure
explaining what cross connections are and how they can be avoided.