When water flows backward through a water supply system. It is called back siphonage or backflow....backflow contamination can be a real problem when water is accidentally mixed with hazardous chemicals or bacteria. The danger of backflow contamination comes when the hose----any hose----comes in contact with a harmful substance.
Then, if the pressure in a water main drops while your hose is submerged in polluted or contaminated water, the water (and whatever is in it) could be sucked back into your pipes and your drinking water supply. Water pressure drops are not uncommon. They can happen when firefighters battle a nearby blaze or before our crew repairs a broken water main.
To protect against backflow contamination, you should buy and install inexpensive backflow prevention devices for all threaded faucets around your home, both inside and outside. These devices are available at hardware stores and home improvement centers. Some examples of how backflow problems arise may help illustrate the problem.
One example is when you spray weed killer on your lawn. If the water pressure drops while you are spraying, the arsenic compound in the weed killer gets sucked back through the hose. If it is a hot day, you may take a drink from the hose after you have disconnected the hose attachment and accidentally poison yourself.
A similar hazard exists if you drink from a hose that has been placed in a swimming pool to add water, or in a bucket of soapy water for cleaning. To summarize, it is important to follow a few simple rules. Do not use spray attachments without backflow prevention device. Never submerge hoses in buckets, pools, tubs or sinks.
Always keep the end of the hose clear of possible contaminant, and finally, buy and install backflow prevention devices for all threaded faucets on the inside and outside of your home.