from link:
Black, Blue, Pink or Purple Water from Mildew, Tank Leaks or Potassium Permanganate
Other colors you may be seeing in your water are black, blue, pink purple. Black water from your faucet is a sign of mildew growth. Blue water likely means the blue disinfectant from your toilet tank is leaking into your regular water supply.
Pink water is likely from potassium permanganate, a chemical used to oxidize iron and manganese. If too much is used your water will turn pink, and if far too much is used it will turn purple. As long as it is still pink it is not a danger to your health.
Polluted Water
It’s possible the water in your city’s system has become polluted. This sometimes occurs after natural disasters, illegal dumping or a malfunction in the city’s filtration system. If your water smells funny like chemicals, human waste or other foul smells, you need to have the problem looked at immediately.
The first call should be to your city water department to inquire what the possible contaminants could be. Then ask neighbors if they have experienced the same issues. If your neighborhood is experiencing an area-wide problem, the city will need to come out an address the issue.
On occasion we get brown water when they are flushing the system. Only lasts a flush or two
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Put a cup of potassium permanganate in a dish and light the center of the pile.
When it is done burning it will look like a little volcano.