I once received a call from a CO-OP that a stock holder was complaining about blue water in her bathtub on the 18th floor.

After checking several apartments above and below this one I found one of the handymen install a ball ***** that was not code approved because it did not have a vacuum breaker.

Because this valve allowed back siphoning the blue chemicals used to clean a tank several floors below flowed back into the domestic water line and went up the riser to this apartment.

Once I replaced and flushed the lines end of problem

I am guessing that you have a low pH and using copper pipes. Is that right?

If so, you would need to neutralize the water by raising the pH by a variety of different ways depending on the pH level.

Blue usually means copper in the water. A water test for copper will tell if it is the cause.

If it is, there are a number of causes; low pH acidic water, high TDS, DO and CO2 content, hot water recirculation systems with excessive velocity, dissimilar metals corrosion, bacteria and electric grounds on copper tubing or a bad building ground etc..

All can lead to pinhole leaks in copper tubing.

Gary

Quality Water Associates

When we put the bath water into a clear glass, the water was clear. It only appears blue. This is what makes me think it's a special coating on the tub.