If you ever ask a plumber if they have had a “blue water” service call, you will probably get a “yes.”  So what is a “blue water” service call?  This is when a customer turns on a faucet, usually in a bathroom, and discovers that they are washing their face or brushing their teeth with “blue water.”  Now, your kids may think this is cool, or they may have a sudden phobia about going into your bathroom. I remember that one of our daughters was 4 or 5 before she would use a toilet with blue water in it.  Her older sister had told her that there were sharks swimming in toilets with blue water.  There were several occasions while at a friend’s home that my wife or I could be found in the back yard cradling our daughter in a swing like fashion so she could potty on the ground because the toilets inside had blue water in them.

There is more than one potential cause for “blue water,” but the most serious comes from a cross contamination within the plumbing system.  This can happen suddenly, and is because the water in the toilet water closet is being sucked, or drawn, into the water supply lines in the home.   The “blue” comes from the blue dye used in cleaning agents many people use in their toilets.   Actually,  any “dirty” or “grey” water, not just “blue water,” could be being sucked into your water lines, and you probably won’t know it if it was not for this blue coloring. Any water cross-contamination can have serious health consequences because of the caustic chemicals found in cleaning products, or just the bacteria found in dirty water.

This cross contamination, or back-flow, can be caused by a defective water pump (if you have a well), a broken water main, or even a fire truck using a neighborhood fire hydrant.  These events can cause negative pressure in your water lines, thus drawing contaminated water into your water pipes.   The first thought that comes to mind is “Yukkk!”  So how do you prevent cross contamination?

1.    Put “back flow preventers” on your outside hose fixture (bibs).  These are available at any hardware store for approximately $5.

2.    Do NOT leave a hose that is connected to a faucet lying in a laundry tub, bath tub, or any other place that “dirty” water could back-feed into your water pipes (like the photo to the right).

3.    Make sure that the fill valve in your toilet water closet is properly installed, and that the water valve has a backflow preventer, or air gap.  Newer valves have a “C L” embossed on the valve (see photos below).  This indicates the Critical Level at which backflow will occur.   The water level in the tanks needs to be 1” below the “C L” level on the valve.  If you still have the old bulb float that turns off the fill valve, you have neither a backflow preventer, nor a built in air gap.  I recommend you install a new one (approximately $15).

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If you have concerns about your plumbing system, give your favorite plumber a call, or call a trusted home inspection company to diagnose your problem.  Just remember, there might be more in your blue water than just sharks.