White water from the tap? Here's the cause

Reading time: ~9 minutes

What exactly is white water from the tap?

You turn on the tap and milky, opaque water comes out. No brown colour, no flakes, no smell, just white. The first thought is usually that something is wrong with the drinking water. In almost all cases, that is not true.

That distinction matters, because in water technology colour says something about the particles floating in the water. Vitens names three colours customers report: blue water, which is clear water with the right light on it, brown water caused by iron and manganese particles, and white water caused by oxygen in the water, especially on warm days. Only with brown water is something solid actually floating in your glass.

At PureFilter, we mostly see this question come in after a fault or street works nearby. Customers are startled by the colour, flush away litres of water and wonder whether they can still drink their tap water. The answer is almost always yes, which is exactly why this article starts with what white water is not.

Why is your tap water suddenly white or cloudy?

There are three causes that together explain the vast majority of reports. All three come down to the same thing: air trapped under pressure in the water that wants to escape again at the tap.

1. Air in the pipe after works

This is by far the most common cause. If work is being done on the main pipe or the connection pipe, the water is shut off and then pressurised again. Waterbedrijf Groningen describes it briefly and clearly: after works, air can get into the pipe, giving the water a whitish colour, and if you let the tap run for a moment it becomes clear again within a short time.

You often notice this together with a sputtering tap or a brief pressure dip. If you are wondering whether something is going on in your street, a local fault is usually fixed within a day. What you should and shouldn't do in the meantime is covered in our article about what to do when no tap water comes out of the tap.

2. Hot water: air expands due to temperature

If the white water only comes from the hot tap, you are dealing with physics rather than a fault. Water always contains dissolved air. When you heat that water, the air expands and is released as thousands of tiny bubbles as soon as the water leaves the tap. Vitens has been explaining this phenomenon for years to customers who report exactly this.

The effect is strongest with water from a boiler or geyser, because that water has been warm the longest. Hot tap water is not a good idea to drink anyway, and that has nothing to do with the colour: according to Evides, too many metals can be dissolved in hot tap water, such as copper from a storage tank or copper pipes, and taps on the hot water side can release nickel, chromium and cadmium. Water companies therefore advise against regularly drinking hot tap water. We covered that in more detail in our article about drinking hot tap water.

3. Oxygen, especially on warm days

The third variant appears with a freshly poured glass on a warm summer day. Vitens literally calls this normal: a freshly poured glass can look white due to oxygen in the water. Cold water can dissolve more gas than warm water, so as soon as cool tap water warms up in a warm kitchen, some of that gas is released. How warm your tap water should actually be, and when a deviation really does mean something, you can read in our article about the temperature of tap water.

The glass test: be certain within three minutes

There is one simple test you can do without any measuring equipment, and it immediately shows the difference between air and something else.

1. Pour a glass of the white water and set it on the table.
2. Watch for three minutes without moving the glass.
3. Watch the direction in which it clears. With air, the water clears from bottom to top, because the bubbles rise. Evides describes exactly that: if you leave a glass of white water standing, you see that it becomes clear again after a few minutes.

When white water is not caused by air

The exceptions are rare, but they exist. These are the three situations in which a white haze means something else.

Limescale: a haze that does not clear

If the water stays milky, you are probably looking at limescale rather than air. According to Evides, water hardness is determined by the amount of calcium and magnesium in it, and that amount differs per source: river water, groundwater and dune water each produce a different hardness. With hard water, after boiling you can see a white haze or white flakes in the kettle, and that is dissolved limescale that has precipitated out.

That is not a health problem, but it is a household nuisance: limescale build-up on taps, in the kettle and in the dishwasher. How hard the water is where you live differs greatly by region, and we looked this up per municipality in our overview of water hardness by municipality. What limescale exactly does to your appliances, and what you can do about it, is covered in hard water in the Netherlands.

White water with an unusual smell or taste

Air is odourless and tasteless. If you smell or taste something unusual with the white water, that is not part of this phenomenon, and it is wise to call your water company. That certainly applies if you have just returned from holiday: if water stands still in the pipes for weeks, a musty or sewage-like smell can develop. Vitens then advises opening all hot and cold taps on returning home and flushing the pipes for a minute. How long tapped water stays good is something we covered in our article about how long you can store tap water.

A boil water advisory in your area

In the event of a fault or contamination, the water company can issue a boil water advisory. That has nothing to do with the colour of your water, but it is the only time you should not simply drink your tap water. Vitens then asks customers to boil the water for a good 3 minutes. Evides points out that most coffee machines do not heat the water to about a hundred degrees for around three minutes, so during a boil water advisory fill the reservoir with water that has already been boiled and cooled again. A boil water advisory always remains in effect for several days, because the water samples need to be analysed in a laboratory.

White water versus brown water

The two reports are often confused, even though the cause and the advice differ. Waternet puts them side by side: white water is water with air bubbles, brown water is water with iron particles. Vitens adds manganese as a second source of the brown colour.

What you can do yourself, step by step

1. Do the glass test. If the glass clears from bottom to top within a few minutes, it's air and you're done.
2. Let the cold tap run briefly. Waterbedrijf Groningen recommends this to get the air out of the pipe. Half a minute is usually enough; flushing longer serves no purpose and wastes water.
3. Ask your neighbours. If they have it too, it's about the street pipe and not your own installation.
4. Check whether works are taking place. Water companies publish current faults and works online, usually via a national outage website.
5. Call your water company if in doubt. If the water stays milky, smells or tastes different, or it lasts longer than a day, the report belongs with the water company. They take a sample free of charge.

What you especially don't need to do: flush away litres of water, buy bottled water or have your entire installation inspected. Dutch tap water is strictly monitored. Vitens states it takes around 200,000 samples a year from source to tap, with around 25 colleagues out in the field daily and a laboratory that processes around 750 samples and 2,500 bottles per day. There are also only 24 to 48 hours between the production of the drinking water and its delivery from your tap. What that means concretely for the quality in your area is something we covered in our article about Vitens water quality.

Does a water filter remove white water?

Here an honest answer is due, even though we sell water filters ourselves. No, a water filter does not solve white water. Air is a gas trapped under pressure in the water, and no filter medium stops that. The bubbles simply pass through the filter housing and still escape into your glass. Anyone who sells you a filter with the argument that it takes away milky water is selling you a solution to a problem that disappears on its own.

What a filter is actually meant for are the substances you cannot see. Colour and clarity say nothing about PFAS, microplastics, pharmaceutical residues or heavy metals: these are all invisible in a glass. That is precisely what makes this question confusing. The water people are alarmed by is usually fine, and the water that shows nothing is what the discussion is actually about.

Evides is level-headed about it too: the water supplied fully meets the requirements of the water supply act, so filtering is not necessary, and if you do use a filter, maintain it regularly to prevent bacterial growth. That last point is a fair one, and it is exactly why our filter intervals are fixed rather than optional. If you want to understand what to look for when choosing a water filter, our pillar page compares the technologies on what they do and don't remove.

What the PureFilter Mineral+ does do

The PureFilter Mineral+ is an under-sink filter connected to the cold water line. It removes more than 100 contaminants in five steps, including PFAS, microplastics, heavy metals such as lead and copper, fluoride, nitrates, pharmaceutical residues and chlorine. The system is NSF certified to standards 42, 53, 61 and 372. As a final step, Swedish Mineral Rock™ adds back calcium, magnesium and potassium, so your water tastes softer and fuller instead of flat.

The order matters here: purify first, then mineralise. That is the difference with systems that remove everything from the water and give nothing back. Installation takes 5 to 10 minutes, you don't need a plumber, and one pair of water pump pliers is enough. A 3/8 connector is included as standard. You later swap the filter cartridge itself using the key supplied with the filter, so you no longer need any tools for that.

A replacement filter costs €65.00 and lasts up to 12 months for 1 to 3 people; for 4 to 6 people, about half a year. The duo with two cartridges costs €115.00. Converted over 15,000 to 20,000 litres, that works out to €0.0033 to €0.0043 per litre, well under one cent. If you'd rather not think about it, the Filter Plan sends the filters automatically on time, for €48.00 for 1 to 3 people and €86.00 for 4 to 6 people. That is a choice, not a requirement: individual filters remain available to order separately.

And if you have a boiling water tap

If you have a Quooker or a similar boiling water tap, something special applies here. Evides notes that water from a boiling water tap is indeed safe to drink, because such a tap has a stainless steel storage tank right next to the tap, so no copper is picked up in the water. What such a tap does not do is remove PFAS, microplastics or heavy metals. The two are not mutually exclusive: a water filter Quooker combination places the filter before the cold water supply of the system.

Frequently asked questions

Conclusion

White water from the tap is air in almost all cases, and air is not a problem. Waternet, Evides and Waterbedrijf Groningen reach the same conclusion: it is not harmful, you can simply drink it, and it clears on its own within a few minutes. The glass test confirms it in three minutes. If it clears from bottom to top, you're done.

Only if the water stays milky, smells or tastes different, or a boil water advisory is in effect, does the report belong with your water company. And if a white haze remains, look at the hardness in your region rather than at a fault.

What white water doesn't tell you is what else is in your tap water. PFAS, microplastics, pharmaceutical residues and heavy metals are invisible, even in the clearest glass. Anyone who wants to do something about that chooses a filter based on certification, not colour. The PureFilter Mineral+ costs €149.00 including the first filter, filters more than 100 contaminants, is NSF certified to 42, 53, 61 and 372, and returns calcium, magnesium and potassium via Swedish Mineral Rock™. You'll find it among the water filters in our shop, and anyone who wants to buy a water filter right away can choose the filter package that fits their household size. With 40 days free returns and a 5 year warranty, you can take your time at home to find out whether you can taste the difference.