I have a standard run of the mill 40 gallon 220v 2-element electric hot water heater that is now giving me all kinds of problems. It is only 8 yrs old and has worked great. There are only 2 people in this householld to use this water heater. In the past 14 months, I have developed dark water problems. The water also smells bad. It come from a rain water cistern. I have burnt out 4 elements in the past 8 months. Coming out they are caked with a lot of build up from the water, I think. I can put in new elements and drain the tank , then I am good for about 3-4 months until the dark water problem, bad smells and caked/built up elements appear. I have never had this problem before. There is also a rod in this tank that also builds up with some kind of a scale-ie build up. I replace this rod that the hardware is more than happy to sell me, without any problem solving on their part. Can any one help me or share their solutions with me??

Galvanic corrosion caused by a poorly grounded water heater and/or joints of dissimilar metals like galvanized and copper without a dialectric union. It could also be electrical in nature caused by leakage currents. The sacrificial anode (pipe) can't keep up.