traitement eau de pluie — personne remplissant un verre d'eau purifiée à la maison cuisine moderne

Rainwater treatment: filtering and purifying for the home

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Key takeaways: Raw rainwater requires rigorous treatment via sediment filtration, activated carbon and UV to remove heavy metals and bacteria. This process protects your health and extends the lifespan of your appliances thanks to limescale-free water. UV treatment is thorough, eliminating 99.9% of pathogens to ensure safe domestic use.

Raw rainwater can carry heavy metals, pesticides and pathogenic bacteria as it runs off your roof. Without proper protection, this free resource risks damaging your installations and posing a genuine health hazard.

We have analysed the best rainwater treatment solutions to purify your domestic water supply and protect your health in the long term. Let’s take a look at the filtration technologies and current regulations to ensure your system is safe.

Rainwater treatment for safe domestic use

Raw rainwater contains heavy metals and bacteria, requiring sediment and UV filtration to make it safe for sanitary use. This non-calcareous resource protects your plumbing and reduces domestic maintenance costs.

To make the most of this free resource without compromising your well-being, it is essential to understand how to neutralise the invisible threats that find their way onto your roof.

Removing pollutants and protecting your health

As it runs off, water becomes laden with soot and atmospheric heavy metals. It also carries bird droppings, bacteria and various plant debris that has accumulated on your roof tiles.

Without rigorous treatment, these pathogens pose a real health risk. Appropriate filtration therefore ensures safe water for domestic use as permitted by current regulations.

You can consult ANSES’s recommendations on washing laundry. This advice is invaluable for ensuring the safety of your system.

ℹ️ Properties of rainwater

Rainwater is naturally slightly acidic and very soft. Whilst this protects your appliances from limescale, pH neutralisation is sometimes necessary depending on storage conditions.

Preserving the longevity of your household appliances

Rainwater is naturally soft and completely free of limescale. This prevents limescale build-up on the heating elements of your washing machines and significantly extends their technical lifespan.

For your fabrics, the absence of harsh minerals makes your laundry much softer. Your skin is also less irritated during everyday activities such as flushing the toilet.

Investing in a reliable system ensures protection for your household appliances. It is a major economic benefit to make the most of this natural and free resource.

traitement eau de pluie — filtre de gouttière installé sur maison avec eau claire

An effective pre-filter at the gutter is the first line of defence against impurities

3 steps to filter out impurities straight from the roof

Even before it reaches your tank, the water must undergo an initial mechanical cleaning to prevent the build-up of organic debris.

Install high-performance pre-filters and gutter guards

The drain grate is a simple grid placed at the top of the downpipe. It blocks dead leaves, twigs and birds’ nests. It is the essential first line of defence against large debris.

The self-cleaning pre-filter is fitted to the downpipe. It separates the water from fine impurities, which are discharged into the stormwater drainage system. The clean water flows into the tank.

For effective rainwater treatment, we recommend the following equipment:

  • Stainless steel drain cover
  • Basket gutter filter
  • Filtering collector with fine mesh

Choose between a concrete or plastic tank for pH

Rainwater is naturally slightly acidic. A concrete tank helps to neutralise this pH thanks to the mineral salts contained in the tank walls.

Plastic tanks (HDPE) are lighter and easier to install. However, they do not alter the chemical composition of the stored water.

The choice depends on your budget and the intended use. Concrete promotes slight remineralisation, which stabilises the water. Plastic tanks often require the addition of limestone at the bottom to achieve a similar effect.

Concrete Tank

Neutralises natural acidity and remineralises the water. Ideal for protecting your health and your pipes.

Plastic Tank (HDPE)

Lightweight and economical installation. No effect on pH, requires the addition of limestone.

99.9%

Of bacteria and viruses eliminated by UV rays.

254 nm

Optimal UV-C wavelength for destroying DNA.

Managing unpleasant odours and regular maintenance

Odours often stem from organic build-up at the bottom of the tank. Annual cleaning of the tank and replacement of the filters remain necessary to keep the water safe.

Rigorous maintenance protects your system and your health. Here is our guide to planning your maintenance work and ensuring everything runs smoothly.

Component Maintenance frequency Action to be taken
Drain covers Annual Cleaning
Pre-filter 6 months Visual inspection
Charcoal cartridge 6 to 12 months Replacement
UV lamp Annual Replacement

Effective rainwater treatment protects your health and keeps your appliances free from limescale thanks to mechanical, carbon and UV filtration. Take action now to safeguard your system and enjoy a pure resource. Finally provide your home with healthy, economical and sustainable water.

FAQ

Is rainwater really clean enough for domestic use?+

In its raw state, rainwater is not clean enough for domestic use. As it runs off your roof, it picks up atmospheric pollutants, heavy metals, pesticide residues and organic debris such as bird droppings or dead insects. These contaminants encourage the growth of bacteria and can cause unpleasant odours.

To protect your health and ensure clear water, rigorous filtration is essential. We recommend at least a sediment filter combined with UV treatment or activated carbon to remove 99.9% of pathogens and chemical micropollutants.

What are the health risks if I use rainwater for my laundry?+

ANSES highlights that rainwater may contain microorganisms and chemical contaminants, which vary depending on your region. The main risk lies in the persistence of these agents on fabrics, which can cause irritation or infections in vulnerable individuals.

Its use in washing machines is therefore not recommended for young children, immunocompromised individuals or those suffering from skin conditions. For others, effective disinfection and strict adherence to washing temperatures are essential to minimise any microbiological risk.

What uses of rainwater are permitted inside the home?+

In France, the regulations are clear: you may use rainwater to flush your toilets and mop your floors. Its use in washing machines is permitted on an experimental basis, provided a suitable and registered treatment system is installed.

Please note, it is strictly forbidden to use this water for showering, dishwashing or drinking. Furthermore, your rainwater system must be completely separate from the drinking water system, with a ‘non-potable water’ sign clearly visible at each tap.

How can I prevent bad smells and cloudy water in my tank?+

Odours usually come from the decomposition of organic matter at the bottom of your tank. To keep the water clear, we recommend cleaning the tank once a year and fitting leaf guards to your gutters to stop leaves getting in from the start.

Using a concrete tank is also an excellent tip, as it helps neutralise the natural acidity of rainwater. Finally, don’t forget to replace your activated carbon cartridges every six months to neutralise unpleasant odours.

What maintenance should I plan for my rainwater harvesting system?+

Regular maintenance is key to ensuring your appliances and system last. You should clean the gutter filters at least twice a year and check the condition of the pump and sediment filter system every six months.

Before winter, the external pipes must be drained to prevent frost damage. A maintenance log should be kept up to date to record every service, thereby ensuring the safety and compliance of your system in the event of any inspections.