In plumbing, a cross connection is one where the city's water supply pipe comes into contact with a source that could contaminate the water. Backflow from the cross connection is what contaminates the water.
The main solution for a cross connection is to eliminate it by isolating each pipe. Also, preventing buildup of water can help prevent problems with cross connections that contribute to backflow. House owners should be aware of any possible places where these connections happen and work to fix them, as they can contaminate the public water supply if left unchecked. Licensed plumbers should be able to solve the problem.