On Thu, 28 Feb 2013 17:40:26 -0800 (PST), "
wrote:

I turned on the hot water in a house that had been empty for a while and got the worst rotten egg smell ever and it continued for 20 min till the hot water ran out. No problem with cold water. It came back after the water heated up again and this is from an electric water heater. any ideas?

We had that problem with a couple of water heaters at work. Turns
out, it is a reaction between the magnesium anode and the water
chemistry. We put in aluminum anodes and the problem went away.

I had never heard of it, but it is a common problem in some areas.