If you turn on your faucet and notice that your water smells like rotten eggs, bleach, or just smells ‘off,’ your gut reaction may be to assume your water supply is contaminated — but that might not always be the case.

Bleach smell – Town waterworks departments typically chlorinate water to prevent bacterial growth. General levels of chlorine in drinking water from public water suppliers range from 0.2 – 2.0 parts per million (ppm), though levels can be as high as 5.0 ppm. Chlorine odours usually go away when the water is exposed to air for a few minutes.

Adding chlorine to the water through shock chlorination of a well or plumbing system produces a strong bleach (chlorine) odour, and the bleach smell stops when chlorine fully dissipates. Sometimes chlorine may interact with organic matter built up in the plumbing system and add odour to the water. Again, the smell should disappear after running the water for a few minutes.

If water is supplied by your own well and the problem appears to be in your plumbing and/or well systems, then your entire water supply system should be flushed by a licensed well driller or pump installer. If you are on a public water supply and the problem appears to be coming from the supply line, contact your town’s water department.

Rotten egg smell – The most common reason for smelly water is caused by water heaters. Bacteria that naturally occur in water can react with the magnesium and aluminum anodes in water heaters and produce hydrogen sulphide gas. If you notice a rotten egg smell when you run hot water but not cold, your hot water heater is probably the culprit. 

Another common cause of rotten-smelling water is because of bacteria growing in your drains. Food waste can accumulate on the walls of the drain and encourage bacteria to grow. You can fix the problem by following these steps:

1. Fill a glass with water from the sink that has the smell and swirl the water around inside the glass a couple of times. If the problem is in the drain, the tap water in the glass should not have a stench.
2. Flush and disinfect the drain by pouring half a cup of baking soda down the drain, followed by half a cup of vinegar. Wait approximately 15 minutes and then flush the drain with hot tap water.

If you have ruled out your water heater or drain as the source of the smelly water, it may be coming from the water source. If your home has its own water well, the groundwater chemistry may be supporting bacterial growth. To fix this, chlorinate the well with shock treatment and pump out the water until the chlorine and rotten egg odours disappear.