HI, I have a friend who has a problem with as he describes it snot coming from his hot and cold water taps, sometimes its like a white jelly type substance and sometimes it can be black and a bit firmer, this is only occasionally and water flow is fine, he has contacted Essex water and they have tested the water and said it is fit to drink and have not given him any idea what may be causing it. He has a combi boiler so no water tank, anyone any ideas?