A.If we leave the water heater unused for a long time or use it at low temperatures, then the water coming out can be malodorous. At times this foul odour can be related to the major water source to the water heater/house, for instance the overhead tanks or underground tanks that store water.
So, it would be simple to see whether the foul smelling water is from the hot water or from other pipes which would indicate that the storage tank is the culprit.
Often, we find discouloured water ( light brown tinge) coming from the water heater, while the rest of the pipes have clear water. This would indicate that there is rust built up within the water heater.
Generally the traditional water heaters(the elements) last for 3-5 years, the newer ones last for 5-10 years ( depending on the use and hardness of water). So, if the life of the water heater is long overdue then we need to consider replacing it.
If the raw water pumped in has high sulfates, then also, we can have foul smelling hot water. Bacteria in the water reduce sulphate to sulphide and can inturn be converted to hydrogen sulfide.
Most conventional water heaters have the anode elements that can produce sulphur, magnesium or aluminium. The anaeorbic bacteria in water react with the sulfur to produce 'HYDROGEN SULFIDE' gas ( the rotten egg or foul fish odour we used to get in our chemistry labs).
Using this water can lead to sense of vomting( because of the foul odour), headaches, irritability or fatigue etc.
B.1.It is not advisable to switch off the water inlet control valve to the heater. If we are returning from a vacation, then the simple thing would be to flush the pipe by allowing them to discharge water for a few minutes.
2. Turn on the water heater and then empty the water a couple of times, this flushes away the sufide and the water with bacteria also.
3. If you have an exclusve supply from an overhead tank to the water heater, then you can add common household bleach to chlorinate the water ( the techniue used in swimming pools and small tanks). Roughly 2 liters of bleach for 150 liters of water. The contact period is around 7-8 hours, then run the water off.
4.If you have a common water connection, the you need to empty around 4 liters of water from the water heater if you have a draining valve and disconnect the inlet pipe, add bleach water via the cold inlet and then allow the contact time to elapse, this is better done by a professional.
5. Hydrogen peroxide (around 500 mls for 75 liter tank) can also be used to get rid of the smell in the water tank/heater.
6. Potassium permanganate is also used to counter foul odour in water because it is a strong oxidant. Around 0.5 mg/liter can help in reducing the water.
C. You can drain the water from the water tank. This is done by closing the water inlet and attaching a suitable plastic/rubber hose pipe to the mouth of the drain valve that is located in most water heaters. You need to check with the brochure of your water heater to see whether this is advisable.