Faecal bacteria in drinking water

First of all, E. coli. This is a bacterium that is commonly found in the guts of humans and animals. It is widespread and easy to detect, which is why drinking water utilities check the water for it. The presence of E. coli means the water may also be contaminated with other bacteria. Although E. coli itself is usually not very dangerous, its presence means that other, more dangerous, bacteria may be in the water that will be more difficult to detect. And so drinking water utilities do not take any risks and they advise boiling the water for three minutes. The E. coli bacteria itself will not usually lead to serious illness but this precaution is taken to be on the safe side, and particularly to protect vulnerable people.

Small amount of E.coli

So is there faecal matter in the tap water? No, certainly not. There has been contact with the water, but the amounts involved are very small. E. coli is found in many places. On toilet door handles, for example. So the boiling notice is purely a precautionary measure in case more harmful bacteria has got into the water.

Is this linked to the water sources, for example in combination with climate change? No, that is not the case. The water in Amersfoort comes from deep groundwater, where there is no E. coli. A combination of groundwater and surface water (the Meuse river) is used in Limburg but the affected area uses groundwater. Surface water often contains E. coli but drinking water utilities treat and disinfect their water thoroughly. E. coli in the source is removed. Last week, the treated water had nevertheless been contaminated in some way.

Clean water in water holding tank

Can’t drinking water utilities prevent contamination of this kind? Drinking water utilities protect treated water as well as possible. It is stored in ‘water holding tanks’, large reservoirs full of clean water that no one is allowed to enter. However, the water must be aerated to stay fresh. There is always a possibility that something might go wrong at times, such as bird droppings being sucked in with the air or a mouse squeezing in through a crack. That can be enough to justify rejecting the entire tank. Other causes may be a cracked pipe, or work on the mains system.

Will this happen more often? Drinking water utilities make every effort to protect their water as much as possible, and so contamination is rare. The fact that any contamination makes the news demonstrates how unusual it is. Even so, you can’t rule out the possibility of contamination completely so it will still happen occasionally. It is entirely coincidental that this happened last week in two regions at the same time.

Bathing in open water

As a comparison, the law requires us to ensure that no more than 1 in 10,000 people a year can fall ill as a result of drinking tap water. This means that a large reservoir of drinking water can include 1 or 2 of these bacteria at most. The standard for bathing in open water is that no more than 5-10% of people will fall ill as a result. Even so, a lot of people seek out open water on hot days and they will sometimes pick up a mouthful. This is a much higher risk than possibly drinking contaminated tap water.

Isn’t bottled water better? Generally not. The requirements for tap water are much stricter than those for bottled water, and tap water is inspected much more frequently. In addition, bottled water can be 1,000 times more expensive than tap water and its environmental impact per litre is 3,500 times higher. So boiling for a few minutes really is the best option for everyone.