How To Inspect Your Own House, Part 7: Protect Your Water by Preventing Cross-Connections

The most important job of any plumbing system is to deliver clean water, and to keep that water clean from sewage and other contaminants. This makes up the first and second of the basic plumbing principles in the Minnesota State Plumbing Code, which read as follows:

A. All premises intended for human habitation, occupancy, or use shall be provided with a potable water supply which meets the requirements of the commissioner of health. Such water supply shall not be connected with unsafe water sources nor shall it be subject to the hazards of backflow or back-siphonage.

B. Proper protection shall be provided to prevent contamination of food, water, sterile goods, and similar materials by backflow of sewage. When necessary, the fixtures, device, or appliance shall be connected indirectly with the building drainage system.

A large section of the plumbing code is dedicated to protecting our potable water supply, so it's a good idea to check your own home for some of the most obvious violations and fix them. Truth-In-Housing Evaluations have a big focus on protecting the municipal water supply, and homeowners are typically required to repair conditions that could contaminate the potable water supply. I've already blogged about many of these conditions, so I'm pulling content from many of those past posts to put all of the information together into one post.

Check out this old video clip for some good information about the importance of protecting the municipal water supply. The first minute and forty-five seconds waxes on and on about who made the video possible, then they get to the actual content, so here's a link to 1:46 into the video: http://youtu.be/ETqvDrPYlsc?t=1m46s

As mentioned in the video, any potential cross-connections are potential sources of contamination.

A cross connection between the water in a toilet tank and the potable water supply can be made if the toilet fill valve or toilet ballcock is improperly installed. There are three most common types of toilet fill valves; the old style ball-cock, the new style fill valve, and the clam-shell type. The ballcock relies on a floating ball to shut off the water supply when the water in the tank gets high enough. The approximate height at which the fill tube connects to the ballcock is considered the "Critical Level" line, and it needs to be at least 1" above the top of the overflow tube. The diagram below illustrates this.

Here's a short video clip that I made many years ago, showing homeowners how to adjust the height of the fill valve in an existing toilet. One quick warning though: the installation instructions for these fill valves actually says to adjust the height of the fill valve before it's installed, and that the little ring on the bottom shouldn't be moved at all, as this is what holds the assembly together under pressure. Whatever.

http://youtu.be/nmZwf5QEbSU

A far less common type of fill valve is the clam-shell type, which sits at the bottom of the toilet tank. These valves create a potential cross connection and just shouldn't be used.

While the risk of contamination to the potable water supply is fairly low, I suspect most people would prefer to not drink the water in their toilet tanks if they didn't have to. While on the topic, here's a 'fun' photo I took during a home inspection a couple of years ago. I flushed the toilet as I was filling the bath tub, and the filthy water in the toilet tank was siphoned into the water going into the tub, instantly turning the tub water black.

Gross, huh? That's why the guts of the toilet matter.

Every faucet I've seen on new construction homes for the past several years has come with built-in backflow prevention, and can be identified by a slightly longer stem. The photos below show examples of faucets with integral backflow prevention. These faucets don't need an external vacuum breaker.

Utility sink faucets with threads that will accept a garden hose should have an exterior vacuum breaker installed. Don't install vacuum breakers at the hot and cold water valves for the washing machine though; washing machines are already built with an internal air gap.

If you have an old bath tub with a faucet located inside the tub, such as the one pictured below, you have a potential cross connection. Don't mind the height of the overflow; the overflow is not the same as the spill line, as a clogged drain would also mean a clogged overflow.

One way to correct this issue is to replace the faucet. A proper faucet for a clawfoot tub will have the opening of the faucet spout located well above the spill line of the fixture, as shown below. I found a decent selection of replacement faucets at http://www.vintagetub.com/asp/tub_faucets.asp .

If you like the faucet you have or you just don't want to change out the faucet, another option is to have dual in-line check valves installed on the water supply pipes. These valves will prevent potentially contaminated water from flowing back into the potable water supply. If you choose this method, make sure the check valves are accessible; when the next inspector comes through, they'll probably be looking for them.

This is a bad setup to start with, because there is no way of tempering the water coming out of the faucets unless you want to fill the sink... and who wants to do that?

The best fix is to replace the faucets with a single faucet, which may also require replacement of the sink. Another option is to install check valves on the water supply pipes.

One non-recommended way to fix this cross connection is to bend the faucets up a little bit to create an air gap. I say non-recommended because there is a risk of permanently damaging the fixtures, but I bring up this fix because I've seen it done many times.

Hand showers that can sit in bath tub or shower water create a potential cross-connection. Many hand showers already come with built-in backflow prevention, but not all. The most obvious way to prevent a cross-connection at a hand shower is to replace the hand shower with a standard shower head that doesn't have a hose.

If you don't want to lose your hand shower, install a vacuum breaker with a 1/2" thread, as shown at right. This device installs in-between the pipe coming out of the wall and the shower head.

If you live in Saint Louis Park or Bloomington, you'll have to fix this when you have your pre-sale inspection done. For Truth-In-Sale of Housing evaluations, Minneapolis only requires that handheld showers have a hook to hang on that will keep the shower head above the spill line of the fixture.

If the dishwasher drain hose is improperly installed, there's a potential cross connection at the dishwasher. The Minnesota State Plumbing Code (section 4715.1250) actually says that dishwasher drains are supposed to have an air gap, which is this ugly thing that sits on top of the counter, as shown in the diagram below (courtesy of CodeCheck).

We don't see too many of those here in Minnesota though (thank goodness), because the plumbing code then goes on to say that a residential dishwasher is allowed to connect directly to a garbage disposer or sink tailpiece as long as "the drain line is fastened as high as possible under the countertop." The diagram below shows a nice example of this:

Nevertheless, here's a common installation that we find, even while doing new construction inspections:

Tsk tsk. As you can see, the dishwasher drain hose isn't even looped as high as the bottom of the sink... and this was from a brand new home in Plymouth that we inspected a week ago. For more discussion on this topic, check out my old blog post on dishwasher drains.

The only problem with the setup shown above is that it will make a big ol' mess of the floor. This next one is a pre-manufactured solution called the Handy GaP, which will prevent water from splashing all over.

If the water softener discharges to a laundry sink, simply figure out a way to make the hose terminate 1-1/2" above the spill line of the sink. The photo below shows one example of this.

In Minnesota, the minimum type of backflow prevention device required for a boiler in a one or two-family home is a double check valve with an intermediate atmospheric vent (DCVIAV). This valve must be installed on the water supply line that feeds the boiler. The image below shows an example of this device.

For anything other than a one or two-family home, a reduced pressure zone (RPZ) valve must be installed. This valve is also needed if any chemicals are added to the system, such as glycol.

If you have a boiler at your home but you can't find one of the two valves pictured above, you ain't right. This is a repair that's best left to a plumber.

Author: Reuben Saltzman, Structure Tech Home Inspections