Off-grid water system: how to make drinking water

Reading time: ~9 minutes

What is an off-grid water system?

Living off-grid sounds like something for a mountain cabin, but in the Netherlands it usually means a tiny house on a plot without a connection, a holiday home, an allotment garden shed or a camper. In all of these situations you have to arrange your own drinking water. That means taking over the tasks a drinking water company normally does for you: choosing a source, treating the water, testing it and storing it safely.

For comparison: according to the RIVM (Dutch National Institute for Public Health and the Environment), ordinary drinking water in the Netherlands comes about 60% from groundwater and 40% from surface water, and is tested daily before it enters the network. You can read exactly how that works in our article on where our drinking water comes from. An off-grid system has to replicate that entire chain on a small scale.

Which sources can you use?

There are roughly three sources of water without a water mains connection: rain, groundwater and surface water. Each source has a different risk profile and therefore needs different treatment.

Rainwater: clean from the sky, dirty from the roof

Rain is naturally soft and contains little lime, but on its way down it picks up substances from the air, such as exhaust fumes, metals and pesticides. On the roof, bird droppings, leaves and dust are added. The Drinkwaterplatform mentions a third problem: soft, slightly acidic rainwater dissolves metals from gutters.

How much you collect is disappointing. According to calculations by KWR (Dutch water research institute) based on KNMI data (Dutch meteorological institute), you can store about half of the rain that falls on a roof in a tank. After deducting roof losses and the first flush, that covers only 25% of a household’s daily consumption, which the Drinkwaterplatform puts at 262 litres per day.

Well water and groundwater: filtered by the soil

Groundwater is rainwater that has seeped through sand and clay for years. The soil holds back a lot along the way, which is why it is also the favourite source of drinking water companies. A private well, however, is something different from an abstraction 100 metres deep. A shallow well can pick up manure, sewage or pesticides from its surroundings, and it often naturally contains iron and manganese.

The RIVM calls such a source a private abstraction (“eigen winning”) and is clear about responsibility: it lies with the owner. The RIVM also warns that quality can deteriorate between the moment of pumping and the tap, and that contaminated water can cause complaints such as diarrhoea, vomiting or fever.

Surface water: only with full treatment

Water from a ditch, canal or lake contains suspended matter, bacteria, viruses and substances from agriculture and sewage. Drinking water companies that use surface water let it flow through dunes or storage reservoirs for months before the actual treatment begins. For a private off-grid system this is the most difficult source, and without membrane filtration and disinfection it is not an option.

How do you turn rainwater or well water into drinking water?

A reliable off-grid water system works with several barriers in series. If one fails, the next still catches something. The order is largely the same for rainwater and well water.

1. You let the first flush run off, because according to the Drinkwaterplatform the first 2 millimetres of rain after a dry spell must be diverted separately to wash dust and leaves off the roof.
2. A coarse pre-filter removes leaves, sand and other large debris from the water before it enters the tank.
3. You store the water dark and cool in a sealed tank, so that no light or heat can get in and algae and bacteria have less chance.
4. A sediment filter or membrane filter removes fine particles and most of the bacteria, and the Drinkwaterplatform names membrane filtration as a suitable technique.
5. An activated carbon filter removes chemicals, pesticides, odour and taste.
6. A UV lamp disinfects as the final step and renders any remaining bacteria and viruses harmless.

After that comes the most important part: measuring. A treatment line only works as long as filters are replaced on time and the UV lamp is on. The RIVM advises owners of a private abstraction to take three steps: know your system, carry out a risk analysis and measure regularly. If you are looking for a filter for emergencies rather than a fixed installation, you will find more in our overview of how a gravity water filter works.

What does an off-grid water system cost?

The purchase is the smallest part of the bill. The Drinkwaterplatform calculates about €1,000 for a rainwater installation, plus about €1,000 per year for quality checks. Replacement filters, a UV lamp and electricity for the pump come on top of that.

Put that next to the ordinary water bill. According to the key figures from Vewin (association of Dutch drinking water companies), people in the Netherlands use 128.1 litres per person per day and the average price is €1.70 per cubic metre. A cubic metre is 1,000 litres, so a litre of tap water costs less than 0.2 cents. You can read more about this in what a cubic metre of water costs. The Drinkwaterplatform therefore concludes that making your own drinking water is not cheaper than tap water for the time being, nor more sustainable given the energy, materials and testing it requires.

Are you allowed to make your own drinking water in the Netherlands?

Yes, for yourself. The Drinkwaterplatform writes that it is not forbidden to drink water from a rain barrel or ditch. There are, however, three limits. You may not supply or give self-made water to others, because according to the Drinkwaterplatform that is an offence. You may not connect it to the drinking water mains, and if a private abstraction does supply water to third parties, then according to the RIVM the same quality requirements from the Drinkwaterbesluit (Dutch Drinking Water Decree) apply as for a drinking water company, with the Inspectie Leefomgeving en Transport (ILT, the Dutch Human Environment and Transport Inspectorate) as supervisor.

For a tiny house that you rent out, or a holiday home with guests, that last point is therefore no detail. At that moment you are legally a supplier of drinking water.

Where are the risks?

Most problems do not arise at the source, but in the system itself. These are the points that most often go wrong.

• Standing water in a tank or pipe is a good breeding ground for bacteria such as legionella, especially if the water becomes lukewarm.
• A filter that stays in place too long can itself become a source of bacterial growth and so do more harm than good.
• Roofing, gutters and tanks made of the wrong material can release zinc, copper or lead into the water.
• Without test results you do not know whether your system works, because a fault in the treatment is usually not noticeable from taste and colour.

You can see how quickly bacteria can cause problems from the advice drinking water companies give when the network is contaminated. Read our articles on enterococci and E. coli in tap water and on legionella in your tap water.

Sources compared

Half off-grid: where does a water filter fit?

Many people who think about going off-grid do not actually want to live without tap water, but do want to be less dependent and drink better water. A hybrid is then logical: rainwater for the toilet, washing machine and garden, and tap water for drinking and cooking. The Drinkwaterplatform names a rain barrel for the garden or the car as an excellent use.

For that drinking water from the tap, a fixed filter under the sink is the step that makes the difference in taste. At PureFilter we regularly get asked whether our filter can also be used on rainwater or well water. The honest answer is no. The PureFilter Mineral+ is made for Dutch tap water and does not disinfect. So it does not belong as the only step on a source that may still contain bacteria.

On tap water, it does what it is supposed to do. In independent tests by Equinox Labs (2026) it filtered all 40 chemical substances tested, from 75% to 99.97%, including 83% to 85% less PFAS and 99.97% less chlorine. In the final filter stage, Swedish Mineral Rock™ adds calcium, magnesium and potassium. It costs €149.00 including the first filter, lasts up to 12 months for 1 to 3 people and you connect it yourself in 10 minutes, as you can see in our guide to installing a water filter.

If you are unsure which type suits your situation, first compare the different types of water filters side by side, or read which filter we call the healthiest water filter and why. If you would rather go straight to a drinking water filter for your kitchen, the range is on one page.

Frequently asked questions

Conclusion

An off-grid water system is technically quite feasible to build, but it is more than a tank with a filter. You take over the tasks of a drinking water company: choosing a source, treating the water in several steps, storing it safely and having it tested regularly. Expect about €1,000 for the installation and another €1,000 per year for testing, and bear in mind that rainwater from your own roof covers only a quarter of your daily consumption.

For most people in the Netherlands a hybrid is smarter: rainwater for the toilet, washing machine and garden, and tap water for what you drink. If you want that drinking water to taste even better, add a fixed filter under the sink. You can find more about us and what we do at purefilter.nl.