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Banishing Smelly or Black Water

That much-hated, rotten egg odor and/or black water in residential hot water lines is due to the reaction of sulfates and micro-organizisms often found in untreated well water and seldom but occasionally in chlorinated water systems.  It is NOT caused by the water heater but by a reaction between unchlorinated water and the magnesium anode rods in the water heater.

The problem can be solved by chlorinating the tank, periodic flushing and/or anode replacement.

Chlorinating the Water Heater:
Eliminate or reduce smelly water by replacing the anode with one of less-active material (magnesium to aluminum) and then chlorinating the water heating system.

Use one gallon of liquid household bleach for every 30 gallons of heater capacity.  The tank capacity is listed on the water heater ID label.  The water heater should be flushed with bleach when:

  • The water supply has become contaminated.
  • As a periodic treatment for smelly and/or black water.
  • When replacing anode rods due to smelly and/or black water.

Flushing Procedure

    • Shut down the water heater and close its cold water supply
    • Drain one (1) gallon of water from the drain valve for each gallon of bleach to be added (one gallon bleach to every 30 gallons of water heater capacity.
    • Remove T&P valve or disconnect the hot water outlet pipe and pour in the bleach.  Let it sit in the water heater for a minimum of one hour.  Drain the entire water heater through the drain valve.
    • Close the drain valve and fill with cold water to T&P opening or hot water outlet opening.  Let it sit for a minimum of 15 minutes.  Drain the entire water heater again.  Reconnect piping or reinstall the T&P valve and open the cold water supply valve.
    • Bleed air from the system and put the heater back into service, then check for leaks and normal heater operation.

An easy trick to reduce the rotten egg smell is to clamp a jumper wire from the hot water pipe to the cold water pipe.  This shorts out the cathodic or “battery” action of the water heater and is effective about half the time.

Other factors that can contribute to smelly water and may also be the fault of the original water composition includes:

  • Magnesium and calcium chlorides leave a bitter taste.
  • Sodium chlorides produce a salty taste.
  • More than 50 ppm of sulfates results in a medicine taste.
  • CO2 content in low PH water creates fizzy or carbonated water.
  • Iron and tannic water have characteristically unpleasant tastes and smells.

Bock Water Heaters


Information Source: Bock Water Heaters