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Why Does My Hot Water Smell Weird?

Most of us don’t really notice the water coming out of our taps until the dreaded day it starts smelling funny. Clean tap water, after all, is one of the major benefits of living in cities with excellent supply systems. A sudden foul odour in the hot or cold water supply might point to a severe problem, and it’s best to investigate it as soon as possible before it gets out of hand.
Here are the most common causes of odours and what to do if your hot water smells bad.

The Most Common Odour Causes

There are four specific smells that tap water might have. Each can point to a different problem, and some might require a significant investment to fix.

Metallic Smell

If the tap water has a metallic smell (or taste) to it, the most common cause is usually the water supply pipes. Old pipes are made from iron or zinc, and their inner coating might be wearing off, causing the water to leech some of the metal. Since the supply lines are constantly pressurized, the water spends more time in contact with the pipes, accumulating more metal. Therefore, it’s not uncommon for fixtures that haven’t been used in a while to have smellier water. However, you should still have the pipes checked out by a plumber. In severe cases, the pipes will rust from the water exposure and might break. The metallic odour usually won’t be a major health hazard, unless you live in an old house that still has the original lead pipes installed. In that case, you’re probably best off replacing the entire plumbing system to bring it up to modern standards and codes.

If only the hot water smells, it could be a sign that the water heater itself is rusting. Unfortunately, once the water heater starts rusting on the inside, there’s very little you can do to help it. The best course of action is to call a plumber and assess whether a fix is possible or if the heater needs to be replaced.

Rotten Eggs Smell

One of the most common foul odours homeowners encounter is the infamous smell of rotten eggs. What you’re actually smelling is a gas called hydrogen sulphide, which is a natural byproduct of organic matter decay and some bacteria. Municipal water may pick up the smell, but it should be cleared out relatively fast by the treatment plant.
If only your hot water smells like rotten eggs while the cold water is fine, then you should check out the water heater. Water heaters can be host to sulphur-reducing bacteria, which take in trace sulphur and produce hydrogen sulphide. It’s possible to eliminate the smell by flushing the water heater a few times. If the problem persists, you might need to sanitize the entire heater with peroxide.
Another, although less common, cause of the rotten egg smell in hot water is the anode rod inside the water heater. If you have a water softener, the water can break down the magnesium inside the rod and produce the gas within the heater. The best way to check for this uncommon problem is to see if your faucets sometimes let air out with the water.
If the cold water smell persists, check the water softener. In some cases, it can harbour sulphide-producing bacteria.

Musty or Mouldy Smell

Usually, if the water smells musty, it’s the entire water supply that’s off. The main cause of a mouldy smell is an algae bloom in the municipal water supply. Modern water treatments will clear out the algae from the water, but the residual smell might transfer to the house’s water supply.
Unfortunately, there’s very little you can do about these problems. If only the hot water smells bad, you should flush the water heater to remove previous deposits and allow it to fill with clean water. More often than not, a musty smell lasts only a few days and then disappears. If the smell persists, look for potential mould around the fixtures since it might be the actual source of the problem rather than the water itself.

Salty Smell or Taste

This problem you’re more likely to taste than smell. A few substances can cause a salty smell or aftertaste, but the most common are chloride ions. They are formed as byproducts of waste management and attract metals to create salts. The most common problems usually boil down to infrequent spikes in water salt content due to municipal water contamination.
In most cases, you should be able to look up your city’s municipal water supply to see if there’s an ongoing problem with tap water. If not, consider having your water tested out by a professional service.

How to Sanitize the Water Heater

If you’ve narrowed down the reason your hot water smells bad to a failing or bacteria-infected water heater, you can avoid an expensive plumber bill by sanitizing it with hydrogen peroxide. Don’t attempt this if you’re unfamiliar with the plumbing system, or you risk damaging the heater. Follow these steps:
  1. Turn off the water heater, unplug it, and turn off the control switch (for gas heaters, turn it to Pilot).
  2. Close the water inlet valve.
  3. Open a nearby hot water faucet and the pressure valve. Drain enough water to allow for an adequate amount of hydrogen peroxide to be poured in.
  4. Remove and inspect the anode rod. If it’s corroded, replace it. In some cases, this can solve the smell on its own.
  5. Pour in a pint (0.568 litres) of 3% hydrogen peroxide solution for every 40 gallons (181 L) of water in the heater. For example, you’ll need about half a pint for an 80L tank.
  6. Open the water inlet valve and let the tank fill up.
  7. Leave the peroxide to sit for about three hours.
  8. Flush the water heater entirely. Repeat this process after 15 minutes.
  9. Turn on the water heater again and resume normal operation.

Call In the Pros for Help

If you can’t figure out why the hot water smells bad, call in a plumber to check out the piping system. It will provide you with much-needed peace of mind, even if the problem turns out to be transient.

Paul S

Paul has more then 20 years in basement waterproofing and plumbing projects experience. Looking for an advice from an expert plumber? Make sure to read Paul's articles about residential waterproofing and plumbing projects in Toronto.

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