The rainwater filter technique used by HOAT consists of a few steps.
First is the fact that the water that needs to be filtered is as clean as possible in the first stage, in order to get the best results. This sounds obvious, and it is. It harder to change a mud pool into drinking water than it is to put recently fallen rainwater into safe drinking water. Furthermore, the filter cartridges have a much longer durability when they are not too heavily loaded. Because of this, we start filtering as soon as the water runs out of the gutter. However, first preparations must be made such as installing new gutters and cleaning and repairing existing and neglected water tanks.



We replace all traditional rain pipes that are curvy and made of thin metal that will eventually start rusting. The new rain pipes are made of PVC and are a lot more sustainable than the old metal pipes.

Old downspout situation with curves  birds nests coming from down spout  new straight downspout situation  New straight downspout situation

We prefer to stay away from the curves in the rain pipes because this gives a better flow and prevents that leaves and other filth hides in the curves of the rain pipes. Another issue with the curves in the rain pipes is that birds fly into the pipes and make their nests in the curves, causing the pipes to clog up. No or barely any curves means a water slide rather than an opportunity to nest.

Second, the rain water passes a leave filter that makes sure that leaves and other coarse material can’t disappear in the storage tanks. This filter also retains cockroaches, lizards, tree frogs and other animals. The leave filter consists of a concrete round bin that’s installed above the tank and underneath the rain pipe. In the concrete bin are two baskets shoved into each other, fitting exactly into the bin. Between these baskets is filter material that only has to be replaced a few times a year.


New concrete lids are poured over the manholes that exactly follow the contours of the tank. This way, the lid fits on the manhole (the opening on top of the tank which provides entrance to the tank for inspection and

cleaning of the tank) like a puzzle piece, and there are no seams or crevices through which small vermin can crawl into the tank. A painted arrow on the lid and tank marks the position of the lid on which it fits precisely on its place. The overflow pipes at the top of the tanks that are meant to let the excess rainwater out of the tank when it’s full but water still falls, feature a net. This way the water can get out of the tank, but the vermin can’t get into the tank.

By installing the leave and garbage filter on top of the tank, we tackle an important problem that used to be common. The internationally used traditional way to prevent filth built up in the gutters during the dry season flowing into the tanks during the first big rainfall, consisted of a system that had to be manually controlled. A large valve that was connected to a rain pipe had to be open during the the first rainfall so the water coming down from the roofs and the gutters wouldn’t fall into the water tanks, but like with a regular rain pipe, fell on the ground. This way roofs and gutters were cleaned before the people could start containing the rain water from the second big rainfall.


Opening the big valves generally didn’t cause any problems, but people usually forgot to turn them off after the first big rainfall and cleaning of the roofs and gutters. This way no water could be retained for months, which led to a shortage of water during the dry season because the water tanks were barely full or completely empty. Also, playful children would open the valves without the janitor knowing. Thanks to this renewed system with the baskets on top of the tanks, every drop of water that falls can be caught.
There is no operating mechanism so the people don’t have to remember something that is important to the functioning of the system.
Children can no longer play with this system because the system is situated on top of the tank.

The Rainwater Filter
The actual filtering of the water happens in a set of 3 filters that together shape the complete filter.
The first filter is a stainless steel 80 micron pre-filter which stops dirt 80 micron and larger. The second filter is a fiber pre-filter which stops dirt 10 micron and larger. The third filter kills the bacteria. This filter contains a balanced mix of high grade activated carbon, copper, and ceramic elements which give out colloidal silver in the shape of ions.
These silver-ions kill bacteria, viruses, algae and cysts, all the while getting help from the released copper-ions.
The copper-ions working together with the silver-ions increases the

bacterium killing effect. The porosity of the ceramic elements creates a huge surface where the silver touches the water.

Recently, an independent laboratory working for the Thai Ministry of Public Health has confirmed that after a period of about one year the water at the schools that have a rainwater filter is 99,99% free of pathogenic bacteria, which means it is 100% safe to drink this water. More about this on the page “test results”

What is colloidal silver and what does it do?
Colloidal silver is very finely divided silver that has been dissolved in (distilled/demineralized) water via electrolysis.

The size of the silver particles is between 0,015 and 0,005 micron. These particles make positively charged silver ions when put in water. The electric charge of these particles destroys the bacteria.

The colloidal silver technique is used i.a. to sterilise water on board of space shuttles and airplanes. Nowadays colloidal silver is often used to prevent the growth of algae in tanks and to kill bacteria.

Now that the water has been filtered and the bacteria has been killed, the water is clean and safe for drinking. The water slowly fills a 100 liter tank on which a float is places that also releases silver ions to the water. This float has been placed to prevent recontamination.

Eventually the drinking water is led to an appealing drinking place where the children can drink. This drinking place is always situated close to the area where children have their lunch. Taps with a green smiley sticker have clean and safe drinking water. We also place two taps with unfiltered water. Not rainwater, but sourcewater. This water is meant for washing dishes and hands. This way the rainwater is used exclusively used for drinking water.

Taps with a red sad face sticker have unfiltered water. We place the taps with unfiltered water to clarify that there is a difference between drinking water and unfiltered water. Thanks to these stickers even the littlest children know which taps they can drink from. There has been made a cut out in the concrete by the drinking tap, so people can fill bottles. The taps are self- closing so they can’t accidentally stay open and waste safe drinking water.

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