What is the most common form of cross-connection?

The ordinary garden hose is used to create the most common form of cross-connection. A hose can be easily connected to the drinking water supply and used for a variety of potentially dangerous applications. An example would be a garden hose attached to a service sink with the end of the hose submerged in a tub full of detergent. Another example would be a garden hose attached to a faucet and the other end lying in a swimming pool. Another example would be a garden hose attached to a faucet and the other end attached to a fertilizer/pesticide handheld sprayer.