We have had this only once and it was also at a place where the water pressure dropped down to 20 psi periodically throughout the day. If you are using any type of water filter, open that up and take a look. Ours was disgusting. Throw the filter away - bleach the inside of the filter canister and install a new filter. Then sanitize all of your incoming lines with bleach ( pour some inside the hose then turn faucets on until bleach water mixture comes thru. Do not run this thru the filter. Let sit for a few hours in the hose, lines and faucets. Then reconnect the filter, water and run water until no longer smells of bleach - don't forget - resanatize your fresh water tank too. We did all this and it's been 3 mo now and no further problem. P.S. - we drained our water heater also, but did not put bleach thru that.