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Composting toilets

To flush or not to flush

Imagine a beautiful river where you could bathe on a hot summer’s day or maybe kayak or let your children play. No. It’s not like that. Rivers in the UK are mainly the vehicles for sewerage outlets and the place where excess amounts of farming fertilisers end up.

Our present system of “flush it away” is a disaster happening now. So many toxic chemicals and materials get flushed down into rivers, past sewerage works and then out into the sea where they create huge problems e.g. Pollution blights UK seagrass meadows.

Compost the waste

Maybe there should be a huge move towards composting toilets, Many parts of the world accept them as standard. They are now covered by the Building Regulations part G 4. In Europe they were developed in Sweden to protect the landscape in rural areas where summer houses needed to handle human waste without blasting through hillsides to install sewers.

One frequently hears the observation about how crazy it is to collect rain water in reservoirs, purify it up to drinking standard, and then use it to flush toilets. The water then has to be removed from the sewage at the sewage works and cleaned up again. This part of the process frequently goes wrong and pollutes the river or shoreline where it is dumped.

The flow of nitrates, phosphates and potassium (in the form of fertilizer) and humus (in the form of peat for gardens) into and out of houses represents a huge cost to the environment, particularly the mining, processing and transport of them and the eventual dumping of them into rivers and the sea. (in case you are not convinced of sewage dumping problems in rivers and at sea check out the Surfers Against Sewage website)

There is quite a lot of interest on the continent (particularly Sweden, Netherlands, Germany and Austria) in urine separating toilets and these are now available here. A New Scientist article makes a strong case for urine separation not only to take the strain off sewage works but also to return the valuable fertilizer chemicals like nitrogen and phosphates to the land.

The Bill Gates foundation has recently put $42 million into a project over several years to develop a toilet that doesn’t need water, mains power or sewerage and that will cost next to nothing to run. One strong contender is the Nano Membrane Toilet finalist for Cleantech, being developed at Cranfield University.

The whole problem can be addressed by the use of composting toilets and on-site grey water treatment which keep the nutrients and humus for the garden. This also results in a 30% reduction in use of water (for flushing toilets).

As a bonus, this results in considerably lower water bills because the sewage element of your water bill is normally based on your water usage. So if you reduce your water usage by 30% (because a composting toilet uses no water) and then get rid of paying for the sewage element (because you are not connected to mains drainage) then your water bill is reduced to a third of what it might normally be. Costings can vary a lot depending where you live in the country.

Remember that water companies charge roughly the same for sewage treatment as they do for supplying water.  (water in = water out) so for every cubic metre of water you use, you will produce a cubic metre of sewage (approximately).

A typical house (with normal flush toilets) uses about 150 litres/day/person which equals 55 cubic metres (that’s 55 tonnes) of water per year per person. Assuming the cost of about £1.40/cubic metre (including standing charges)  then this would cost about £77. per person each year. Getting rid of a flush toilet reduces the water usage from 150 litres down to 100 litres per day per person.

The cost of handling the sewage (per person) would be roughly the same at £77. (for some reason they charge roughly the same for supplying pure water and for handling sewage)

Total cost about £154 per year per person.

If you remove 30% of the water cost (flushing) and all of the sewerage cost (because you are not connected to main drainage) the total bill is £46/person/year for the water and zero for the sewage and this makes a saving of £108/person/per year. So a 4 person household would save about £432/year. This is fairly handsome reward for the extra initial cost and the (maybe) 4 hours per year spent servicing the toilet. Added to that are all the environmental advantages of cleaner rivers, streams and beaches and the retention of fertilizers in the ground.

Composting toilets tend to be of two types
  • very low flush type
  • waterless

The advantage with the very low flush type (such as the Aquatron) is that the waste can be transported horizontally through the house via pipework whereas with the waterless type it has to drop vertically. This helps if there is a problem with vertical alignment between bathrooms and composting area. The drawback is that the flushing water (which is black water) has to be dealt with somewhere on site if there is no main drainage connection and this is a bit more difficult than dealing with grey water.

More about the Aquatron

Waterless toilets

There are five good reasons for using waterless composting toilets

  • No water is wasted in flushing and hence there is no need for the complex process of separating solids from water at a sewage works. With normal toilets, about a third of the household’s water consumption goes on flushing.
  • There is no chance of sewage entering rivers. It is not unusual for sewage companies to dump raw sewage into rivers when sewage works get overwhelmed during periods of flooding.
  • Fertilizer is not lost to rivers and the sea. It can be used locally
  • There are no smells in the bathroom because a fan keeps the toilet under negative pressure.
  • The fact that human waste does not get mixed with grey water means that the grey water is easy to deal with on site by using a reed bed or leech line

Points 2-5 also apply to some extent to very low flush types.

There are five possible arguments against their use, depending on which particular design is used.

  • They may take up potentially valuable building space (maybe about 4 sq. m. for a Clivus)
  • They may be more expensive than normal loos
  • They may use electric power
  • They may partially dictate the layout of the building (in the case of such as the Clivus)
  • They usually need some degree of maintenance

Waterless composting toilets are basically of two types

  1. those which have no mechanical or electrical assistance, relying on one or two large plastic containers on the floor beneath them in which the waste slowly breaks down over a few years. A slight variant of this is the waterless evaporating toilet such as the Woo Woo which uses radiant heat from the sun to create air movement and evaporation.
  2. those which have electric heaters and stirrers which greatly speed up the process. They usually have a small container built in to the base so they can be situated almost anywhere where a vent pipe can be fitted. They may have removable plastic bags which biodegrade.

The first type uses no energy (except for a tiny fan – maybe 4 watts –  which extracts air up a vent pipe to prevent smells). They produce a compost which is similar to peat and can be spread on the garden (but not onto growing vegetables). Access is needed to a cellar or space below the bathroom. They were originally developed in Sweden for summer houses where it was environmentally undesirable to blast holes through mountains for sewer pipes. Since then they have been developed to a high standard with various sizes available. Examples are the Clivus Multrum and the Envirolet (waterless remote). The second type do tend to consume rather a lot of electricity.

Due to the composting toilet market in the UK being so under-developed the Clivus is not available for the domestic market here and this has led some self-builders to construct their own based on the original Clivus design as found in the books ‘The Toilet Papers” and ‘Sanitation without water’

The picture shows a Clivus ‘clone’ being built of 19mm BCX plywood (which then has a substantial surrounding structural softwood frame). The inside is lined with a thick layer of GRP similar to that used in boat construction. A 4 Watt extract fan keeps air moving in through the seat area and out of a flue on the roof (similar to a normal SVP). The bowl and drop pipe are made using the Swedish Separett urine-separation kit mounted on a vertical section of 300mm plastic land drain.

Some online links

The Humanure Handbook is an excellent on line source of information. Also at Joseph Jenkins IncClivus

the renewable energy centre

Clivus Multrum


EcoTech Products



Biolan Naturum

The Nonolet from “The 12 Trades” (has English translation)

The Moonstone house project has a good video showing how the Aquatron works


In the United States see the Eco-toilet Center.


The Composting Toilet System Book. A Water-saving, Pollution-preventing Wastewater Solution by David Del Porto, Carol Steinfeld, (Paperback Feb 1999) from £41.27

Goodbye to the Flush Toilet. Water-saving Alternatives to Cesspools, Septic Tanks and Sewers by Carol Hupping Stoner (Paperback 22 June 1978)

Reed Beds: For the Treatment of Domestic Wastewater (BR 420)

Price: £40.00

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