layers for water filter

This time ’round we are looking at a more developed type of rainwater filter.

This second type of filtering is a multi-layer filter and is incredibly effective, giving clean potable water and it lasts a long time before you need to empty the barrel and add new filtering layers. It would definitely benefit from a second barrel as storage for kitchen use as well as for drinking water. I would suggest using a second domestic filter for drinking water that is not going to be boiled, just to be on the safe side. Western Green, an Irish company do a great range of filters that suit volume (and pocket) concerns.

The barrel filter is made, as seen in the illustration, in four layers:

The first barrel needs to be raised quite high if you are to keep the cost down and not have to install a pump but if you get into high volume storage a pump will be a necessity and, if you shop around, not extravagant in cost. The second barrel, the reservoir, needs to be largely below the tap onn the filter barrel so there won’t be any problems with pressure or draining.

The layers:

I’m a great believer in charcoal filtering. It’s completely natural and can be bought sustainably (or made but that’s a whole different story…). It’s been used in air and water filtration for a long time. You can make a sand filter but a layer of charcoal really takes out tiny particles that you won’t want in drinking or washing water.

-The bottom layer in the barrel is at least 25 centimetres of gravel, but a little more in a large barrel. It allows a reasonable amount of water to pool for tapping where as sand would be very slow draining and take up a lot of space.

-The next layer in is sand, at 25 to 35 centimetres. It filters out any charcoal that might run down but is also a general back-up filter.

-The third layer to put in is charcoal and is, in my view, the most important layer, filtering out micro-organisms and small particles of dust and indeed anything else that might wash down from your roof. It should be about 10 to 15 centimetres; anny more is just redundant and a bit wasteful. If you have lump-wood charcoal, pout it onto the sand and beat it down. It doesn’t need to be powdered as such but if there are a lot of gaps the filtering will not work properly. It might be a little hard to believe that this scruffy looking layer is going to clean your water but it works a charm!

-The top layer of the barrel is at least 25 centimetres of gravel. This traps large pieces of debris like bits of leaf and such that can be skimmed off when needed but also it allows a pool to form to cut down on the risk of overflow during heavy rain.

Choosing your charcoal

It’s really important to pick good charcoal. You can go nuts and buy specialist powdered charcoal on-line for a small fortune or you can just buy it local. If you spend a little time you can find a supplier who makes their own charcoal and will give you appropriate sizes at a good price (partly because the tiny pieces that you can use have limited use for cooking or running  a traditional forge). However if you are buying in a shop, like most of us will, you need to keep a couple of things in mind. Never use pressed nuggets as they are made with all sorts of bits and pieces and usually have stuff added to bond the dust together. They are also dosed with flammable liquids like paraffin which will affect your water quite seriously. Also never use ‘easy lite’ lump-wood charcoal because it is, again, dosed with flammable chemicals. Ask in your local DIY for lump-wood charcoal that you can open and smell or at the very least read the packaging or go on-line and look at filtration sites or blacksmithing supplies (blacksmiths don’t like chemicals in their charcoal either).

Next week we’ll take a brief look at maintenance and storage and I’ll link to some FAQs that will help (a lot) if you go ahead and put a rainwater harvest system in.


Image credit to

0 replies

Leave a Reply

Want to join the discussion?
Feel free to contribute!

Leave a Reply

Your email address will not be published. Required fields are marked *