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4 Tips On How To Purify Rainwater – Where You Need To Start

When rainwater first begins its life having just been evaporated from the surface of the planet, it is indeed pure H2O. But as it rises into the sky and forms clouds, it mixes with other substances present in the atmosphere, such as dust, pollen, spores and so on. Then it falls on your roof and mixes with even more material, including bird droppings, before being washed down a pipe to your rainwater harvesting system. That might be just a simple water butt at the bottom of a drainpipe that you use to water the roses, or it could be a more sophisticated system that provides water for WCs, laundry use, industrial processes etc.

Potable Vs Non-Potable Water

There is a significant difference between the standards required for garden irrigation compared with drinking water. Potable water must exclude such material and also pathogens and microbial pollutants before it is considered suitable for bathing, washing dishes and drinking. Usually, all the water we use goes through the necessary treatment steps to produce potable water. With a rainwater harvesting system, only basic filtration of particles is generally required to give water that is sufficiently clean enough for flushing toilets, washing clothes and watering the garden.

Rainwater Vs Groundwater

Rainwater is usually considerably cleaner than groundwater in most parts of the UK. The reason being that groundwater can contain run-off from roads, industrial and commercial premises, as well as from agricultural activity and fertilisers. It will also often be discoloured from the soil which it passes through. By contrast, water obtained through boreholes from aquifers deep underground may be as pure as, if not purer, than rainwater if it has filtered down through many layers of rock and stone. Of course, in limestone areas of the country this water may also be very ‘hard’ due to its high lime content. However, rainwater will always be soft with a typical pH value of 5.6.

1. Preventing Algae & Bacterial Growth

Warmth and light promote the growth of algae and other organisms. Therefore it is important for above ground storage tanks to be constructed from an opaque material and if possible shielded from direct sunlight. Good insulation which provides frost protection for the winter months also acts to keep things cool during summer.

2. Primary Filtration

Even if all you use is a water butt, a simple first step that keeps larger material out of your rainwater storage system will ensure your water stays fresher for longer. Filtration can be as simple as some form of mesh or strainer fixed across the inlet to your storage system and cleaned regularly. Better still is to use a proprietary filter, preferably a stainless steel one for performance and durability.

3. Sedimentation

A certain amount of sediment is unavoidable in any harvesting system, as the technique relies upon water passing through a mesh or grill under gravity. There will always be some fine particles that get through, depending on the grade of the filter. Obviously the finer the filter, the less material will get through to the tank, so ideally the filter should remove anything larger than 1mm, and smaller if possible. Good quality filters will filter down to less than 0.5mm, so the collected water appears as clean as tap water. The best filters such as the Vortex filter are almost self-cleaning, requiring attention just a few times each year, and have the added benefit of introducing oxygen into the water. A simple calming arrangement that ensures the water is taken to the bottom of the tank will minimise the disturbance to any sediments that do accumulate. An outlet pipe that takes water not from the bottom of the storage tank but from some point further up will avoid any sediment getting through. Even though fine sediment will build up in the tank over the years, this will not cause a problem if these simply steps are taken.

4. Advanced Purification For Potable Water

An ultra violet light source in the form of a UV Filter is a very effective method of removing the threat from pathogens and microbial organisms. It works by destroying the DNA of the organisms, thus rendering them harmless. For a UV filter to work effectively, minute particles must first be filtered out by a particulate filter to prevent organisms being ‘shaded’, which would not then be exposed to the UV light.

Carbon filtration is sometimes added to improve the taste of the water, depending on the vessel the water has been stored in, but this is optional and a matter of personal preference.