Tap water tastes or smells of chlorine, TCP, earth or eggs: what it means

Tastes or smells of chlorine or a swimming pool

Chlorine is the most common way of disinfecting drinking water. Suppliers keep a small amount in the pipes so the water stays protected on its way to your tap. The Drinking Water Inspectorate (DWI) says companies typically keep this residual at 0.5 mg/l or less, but levels are sometimes higher during maintenance work on the pipe network, which is a common reason for a short-lived stronger taste. Some supplies use chloramine (chlorine combined with ammonia), which lasts longer in the pipes; Scottish Water, for example, says more than a quarter of its customers receive chloraminated water.

What DWI suggests:

• Put a jug of tap water in the fridge for a short time. This reduces the chlorine taste and smell.
• Throw away unused water after 24 hours and clean the jug regularly.

There is no numerical legal limit for chlorine residual in Schedule 1 of the Water Supply (Water Quality) Regulations 2016. DWI says most companies aim to keep it below 1 mg/l, well below the World Health Organization’s guideline maximum of 5 mg/l. Suppliers monitor it to control disinfection and taste, and a lower number is not automatically better. WaterGrade shows the chlorine residual results that suppliers publish, where we hold them.

Tastes of TCP, antiseptic or medicine

DWI explains that a TCP-like, antiseptic or medicinal taste comes from chlorine reacting with chemicals in kettles or in rubber or plastic parts of your plumbing. It can be stronger once water has been boiled or left to stand in a glass. DWI also says a washing machine or dishwasher connected without a non-return valve can cause it.

Checks you can make:

• Taste water from the cold kitchen tap in a clean glass, not from the kettle.
• Check whether the taste only happens from one tap, or after water has stood in a kettle or bottle.
• Check that appliances have non-return valves fitted where they connect to the pipework. A WaterSafe-approved plumber can advise.

Tastes musty, earthy or mouldy

DWI says a musty or earthy taste often comes from water that has stood for a long time or warmed up in little-used pipes, where harmless natural bacteria or fungi can grow, especially on rubber fittings. Running your taps for a few minutes brings through fresh water. DWI also says rivers and reservoirs sometimes develop a musty or earthy taste in summer because of natural processes such as algae growth. If only one tap is affected, the cause is more likely to be in your home.

Smells of rotten eggs, stagnant water or sewage

DWI suggests a simple test: fill a glass with water and take it into another room. If the rotten or stagnant smell has gone, the problem is likely to be the sink or drains, which should be cleaned or unblocked. If the water in the glass still smells away from the sink, DWI says this could indicate a problem with your plumbing and you should contact your water company straight away.

Metallic, bitter or other tastes

DWI says water that stands in copper, iron or galvanised pipes, tanks or fittings for long periods may pick up a metallic or bitter taste. Read our metallic taste guide. For discoloured or cloudy water, see our guides on brown water and cloudy water. Hard water can taste slightly different because of its minerals; check your water hardness.

When to contact your water supplier

• The taste or smell is sudden, strong or unusual.
• It comes from the cold kitchen tap and does not go away.
• Neighbours notice it too.
• It comes with a change in colour or cloudiness.

Your supplier can investigate and, where needed, take a sample. Tell them when it started and which taps are affected. Supplier annual reports include taste and odour results for supply areas, but these summarise past samples and cannot explain a change at your tap today. If you feel unwell, contact NHS 111 or your GP.