My house uses pvc pipes from over head tank for domestic purpose like bathroom , kitchen etc,, the water used to come with good pressure in starting , but now after 5 years the pressure has decreased very much , water out put is very low at the taps . The water that flows in it is under ground(bore well) water(salt content is high). It has become a big problem as we can use only 1 tap at a time that too with a low amount of water coming out of it because if the other taps opens then there will no or very less water coming in the tap.when I removed the tap I found that there is a black color lining on the inner surface of the pipe I thought it will be some kind of accumulation of impurities and thought if I run dilute HCL through the pipe and cleaned all the taps, but nothing worked. Please help