Blue, Green or Pink Tap Water: Should I Drink It?

Blue water from the tap usually has an ordinary explanation, and it is often not a problem with the mains supply at all. In a new building or after new plumbing, small amounts of copper can dissolve into the water until a natural protective layer builds up inside the pipes¹. It is quite common in newly installed pipes and boilers, and it can take a few days for the water to run clear². Run the tap for a few minutes and see whether it clears³.

The exception is bright blue, green or pink water, which can mean water from your toilet cistern has got into your supply. Coloured cleaning blocks in cisterns create brightly coloured water, and faulty or poorly installed plumbing can let it siphon back into your internal pipes⁴. If that is what you are seeing, stop using the water and contact your water company immediately⁵.

So the first question is not "is blue water safe?" but "where is the blue coming from?" A faint tint that clears when you run the tap is one thing. A bright colour that comes back, or that appears at one tap only, is another, and it needs a phone call rather than a guess.

Blue tap water is usually natural and safe to drink

A blue tint in a full glass is often nothing to worry about. Scottish Water says water can look blue because it comes from a high quality treatment works, or from a high quality spring or borehole with very little or no organic content, which is normal and typical of water free from natural colour⁸. In other words, very clear water can pick up a blue cast from the glass or from the light, without anything being wrong with it.

The more common household cause is copper. Most household pipes are made from copper, and in buildings with new plumbing small amounts of copper can dissolve into the water⁹. In very new buildings, or buildings with new plumbing, this continues until a natural, protective layer builds up on the inside of the pipes¹. It is quite common in newly installed pipes and boilers as that protective film forms, and it can take a few days for your water to run clear².

What to do is simple. Run your tap for a few minutes until the water clears before using it, especially after new copper piping has been installed³. If the discolouration is caused by copper leaching into the water, running the tap should clear it and reduce the level of copper⁷. If it has been going on for several weeks, Affinity Water advises contacting the company who built or renovated the property, or an approved WaterSafe plumber, and telling the water company's fitting regulations team if you have a water softener¹⁰.

There is a limit to this reassurance. WaterSafe is direct: if your water is blue, do not drink it or use it for cooking until you have sought advice from your water supplier⁶. Bristol Water says it is not advisable to drink water that has an unusual, bright colour⁷. So a faint tint that clears is one thing; a colour that persists is a reason to pick up the phone.

Pink, blue or green water from one tap: check the toilet cistern

Bright blue, green or pink water is a different matter, and the usual culprit is in the bathroom. Coloured cleaning products in toilet cisterns are a recognised cause⁴. Toilet disinfectant blocks create brightly coloured water in a variety of colours, commonly blue, green or pink, and incorrectly installed or faulty plumbing connected to the cistern can let that water get into your supply, usually following pressure changes caused by burst water mains and planned works⁵.

The mechanism is backflow. A faulty toilet cistern or poor plumbing can cause water to flow back from the cistern to your taps³. Poorly installed cisterns can allow water to siphon back into the internal plumbing⁶. Blue-looking water can also result from back syphonage from the cistern, where blue loo blocks and depressurisation combine to produce blue water at the taps¹. Yorkshire Water names the same cause for green water: blue disinfectant in the toilet cistern siphoning back into the internal plumbing¹¹.

If the water is bright green, blue or pink, suggesting water from your toilet cistern has got into your supply, Wessex Water says to contact it immediately⁵. WaterSafe points readers to the Water Regs UK website for information on how to check a toilet cistern⁶. If you are worried about copper pipes in your home, Thames Water advises contacting a plumber¹².

When to stop drinking coloured water and call your supplier

The rule across the water industry is consistent. If you have blue, green or any other coloured water coming from your tap, stop using it until it has been tested². If your water is blue, pink, green or any other colour not otherwise described, do not drink it or use it for cooking until you have sought advice from your water supplier⁹. United Utilities gives the same instruction for blue, pink, green or any other unusual bright colour¹³.

This matters most for the people least able to judge the risk. The London Resilience Partnership advises that if your water is discoloured, cloudy or smells, you should check with your water supply company before drinking it or using it to make baby formula or brush your teeth, as it may be contaminated¹⁴. The same caution applies to anyone preparing feeds for a baby.

Contacting your supplier is straightforward. Southern Water, for example, asks customers who experience blue water to call straight away on 0330 303 0368 to report it². Your own supplier's number is on its website and usually on your bill. If you have a private supply, such as a well, borehole or spring, the route is different: your local council regulates it, and GOV.UK advises contacting your water company, or your local council if you have a private water supply, if your tap water is not clear and does not smell right¹⁵.

Coloured water that is not blue: brown, orange and cloudy

Not every colour change is a copper or cistern problem, and knowing the difference helps you decide how quickly to act. Brown water can be caused by naturally occurring deposits of iron and manganese found in cast iron water pipes¹⁶. Brown water from the tap may indicate slightly higher iron levels, and black particles may indicate a higher level of manganese². A yellow, brown or orange colour is normally caused by disturbance of sediment, mostly iron particles, in the water main, and can follow a burst main or use of a hydrant by the Fire Service⁷.

For brown, black or orange water, the Drinking Water Inspectorate's advice is that in areas with a known iron or manganese problem, if you have run your tap until the water becomes clear it will then be safe to use, unless your supplier has issued a warning notice to say otherwise¹⁷. Thames Water suggests flushing the tap at the highest flow for 2 to 3 minutes, and contacting a plumber if the colour does not clear¹².

Cloudy or white water is usually air, not contamination. Fill a glass and let it stand for a few minutes; if the water clears from the bottom upwards, it contains trapped air¹⁸. If it is air, the glass will clear from the bottom upwards as the air rises to escape from the surface⁷.

After an outage, a flood or a holiday

Colour problems often follow a disruption, and the response is slightly different each time. After a supply interruption, the government's preparedness campaign advises running the cold tap nearest to your stopcock, usually under your kitchen sink, for a while to see if it clears the discolouration, and contacting your water provider if problems continue¹⁹. Running the taps helps flush discoloured water through the system²⁰.

After a flood, contact your water company if tap water is discoloured or tastes bad²¹. The Met Office's post-flood guidance is blunt: stop drinking your tap water if you notice a change in colour, taste or smell²².

After a holiday, blue or green water is more likely because it is often noticed when water has sat in pipework for a long time, for example after returning home⁵. Running the tap for a few minutes is the first step³.

If your supply has been off, the general rules for bringing it back into use apply, and our guide to what to do when your supply comes back on sets them out. If you have been told to boil your water, see what to do if you get a boil water notice. For the wider picture on colour, cloudiness and taste, our pages on brown or discoloured tap water and cloudy or milky tap water go further.

Spring, borehole and private supplies

If your water comes from a spring, borehole or well rather than the mains, the colour question has a different answer and a different route to help. Blue water can be a sign of quality: it may be because your water is from a high quality spring or borehole with very little or no organic content, which is normal and typical of water free from natural colour⁸.

But private supplies are not monitored by a water company in the same way, and problems should go to your local council. GOV.UK advises contacting your water company, or your local council if you have a private water supply, if your tap water is not clear and does not smell right¹⁵. In Northern Ireland, discoloured drinking water should be reported to Northern Ireland Water²³. In Scotland, if you are persistently receiving discoloured water at a mains-fed tap, you should contact Scottish Water so it can investigate and resolve the problem²⁴.

Our guide to private supplies: wells, boreholes and springs covers testing and treatment in more detail. If you are storing water for an emergency, the rules on storing tap water safely at home and how much drinking water to store per person apply whatever your source.

How to report coloured water and what happens next

Reporting is quick, and the more detail you give, the faster your supplier can work out whether the problem is in the mains or in your home. Before you call, note the colour, whether it affects one tap or several, whether the hot water is affected too, and how long it has lasted.

A useful check is to compare with a neighbour. If your neighbour's water is clear, or if only your hot water is affected, it is likely to be a plumbing problem⁷. That points you towards a plumber rather than the water company. Bristol Water recommends choosing a competent and qualified plumber using the WaterSafe scheme⁷.

• Bright blue, green or pink: contact your water company immediately⁵
• Brown, orange or yellow after a burst or hydrant use: run the tap, and call if it remains discoloured after several hours⁷
• Persistent discolouration at a mains-fed tap in Scotland: contact Scottish Water²⁴
• Discolouration in Northern Ireland: report it to Northern Ireland Water²³
• Private supply: contact your local council¹⁵
• After a flood: contact your water company if tap water is discoloured or tastes bad²¹

If your supplier issues a warning about your supply, follow it. The Drinking Water Inspectorate explains that tap water in the UK is safe to drink without boiling because it is treated and continuously monitored²⁵. Our guide to do not drink and do not use notices explains what those notices mean in practice.