: We had a new gas water heater installed about 5 months ago. Now our hot water has a greyish cast and when I filled a bathtub last night the water was very dark grey, almost black. Our house was built in the late 50s. Is this due to the water heater? We have a water softener–could it be something wrong there? The cold water is not affected. Also, do we call a plumber, the person who installed the water heater or the water softener company? Thanks.This sounds like iron bacteria which like hot water systems where water soluble iron exceeds 0.2 parts per million. Your plumber would be the one to handle this. Check A. O. SMITH WATER PRODUCTS COMPANY for their bulletin # N-101 and # N-102. These will explain possible cause of problem and how to treat it. good luck, blm189