Of all the utilities supplied to your house, water might be the most important. You can be without electricity or natural gas for a long time, inconvenient as that might be. But you have to have water. And your water utility service works hard to supply you with clean drinking water. One of the ways they do that is by creating rules that reduce the likelihood of any contaminants being sucked back into the fresh water supply through your supply pipes. And that’s where cross connections come into play.
A cross connection is any actual or potential connection between a potable water supply and non-potable water.
Way back in the day most bathtubs and lots of sinks had their spout inside the tub or sink, below the flood rim. Like this.
So when the tub or sink was full of water it would cover the outlet of the faucet. Then if the city water system has a loss in pressure this can allow the dirty water in the tub to be sucked back into the city’s fresh water system. This is a cross connection – a potential connection between the potable water supply and non-potable water. A loss in pressure is a rare thing, but it has happened and the results can cause a huge disruption for all the people who get their water from that system. A loss of pressure can happen if a water main breaks, or if the fire department starts using a lot of water to fight a fire. So it’s not just a hypothetical scenario.
Plumbing codes now require the outlet of a faucet to be above the flood rim of a tub or sink. And this has been the rule for many decades, so if you see a tub with a cross connection it means that there hasn’t been any significant renovation to this bathroom in a very long time. For most tubs you can buy a replacement faucet that has the outlet loop up above the flood rim of the tub, like this.
There are other places where cross connections can occur that you should be aware of. One place is at your outside hose spigots. If there’s a hose attached and the end of the hose is laying on the ground – maybe in a puddle of water – then that’s also a cross connection.
Or if your hose is connected to a spray device that contains fertilizer or poison (!) that’s a cross connection. So hose spigots now are required to have vacuum breakers built in. A vacuum breaker is a device that prevents water from being siphoned back into the water supply, and it looks like this when it’s built into a hose spigot.
Some cities around me require as a condition of the home’s sale that any older hose spigots that don’t have this feature be replaced with the type that has a built-in vacuum breaker. You can also get a separate vacuum breaker and simply screw it onto your older hose spigot to provide basically the same level of safety.
Another place where I see a cross connection on a regular basis is at a basement laundry sink. Lots of people attach a short length of garden hose to the faucet, and then the hose just lays in the sink. This is clearly a cross connection, and I urge you not to do this.
Another very common cross connection is with an underground lawn sprinkler system. Obviously all the sprinkler heads are a potential source of ground water (which might contain fertilizer, poison, or something else bad) being sucked into the potable water supply. So all lawn sprinkler systems must have a backflow valve installed to prevent water from backflowing into the city’s water supply. Some cities around me require that this backflow device be checked every year by a licensed plumber to ensure that it’s working properly. If you have a lawn sprinkler system I urge you to get your backflow device checked. The company that does your fall shut down service should be able to take care of that for you. Be sure to get a copy of the plumber’s report stating that the backflow device passed its test.