According to the U.S. Environmental Protection Agency, the average American family of four uses 400 gallons of water in the home and garden per day. Of that, as much as 27 percent can be down to toilet use alone. When you consider that the standard modern toilet uses an approximately 1.6 gallons of water for each flush (with older models sometimes using as much as 7 gallons) it’s easy to see how it adds up.
Because water is not (as many people think) an infinite resource, such levels of use are going to be unsustainable in the long-term. Permaculture emphasizes the preservation and efficient use of water on the land (through mulching, planting native species, contouring, and so on) and in the home (taking showers rather than baths, reusing bathwater for irrigation, and similar techniques).
One significant step towards conserving water is the use of a composting toilet. For some people, the thought of a composting toilet is a step too far, imagining that they are smelly or unhygienic in some way. But, in fact, composting toilets are very sanitary and do not smell if treated correctly. They are water-less or use a very small amount of water compared to conventional lavatories (and those models that do have some need for water can easily be serviced by rainwater harvesting).
The other benefit of a composting toilet is, as the name suggests, they provide material for composting. Such a sanitation device serves to create a ‘closed loop’ system, which fits in with the principles of permaculture by being a self-sufficient system, not requiring any outside inputs. Consider that we eat plants for food, that food produces waste, then, with a composting toilet, the waste goes towards growing more plants. These sorts of closed system are found so often in nature, so it makes sense to replicate them on our permaculture plots wherever possible.
Pre-fabricated composting toilets are becoming increasingly available on the market, but the permaculture gardener could also consider constructing their own version. Here are some tips for composting toilets.
The best set-up for a composting toilet is to have two tanks: one for liquid and one for solids (you could have a pump that diverts one from the other, but having separate tanks is the easiest method). This is because urine can be used on the garden immediately, while feces must be composted.
When expelled, urine is sterile and full of nutrients. It contains most of the potassium, phosphorous and nitrogen that our bodies get rid. And in a marvelous piece of symmetry, those are three of the most important elements for plant growth. The reason to split your composting toilet is that urine can be contaminated if it comes into contact with feces; if kept separated, it can be used straight away on the garden, with no need for composting. Dilute one part urine to six parts water (rainwater, where possible) and add to garden beds. You need a tight-fitting lid over the urine receptacle in the toilet, as contact with oxygen in the air can turn the nitrogen in the liquid into ammonia, which will not only burn you plants, it will make the toilet smell.
Feces, on the other hand, must be composted before it can be used on garden beds. When it is initially expelled, it can contain microorganisms and bacteria that are harmful to human health, and if put straight onto the garden, these organisms can be taken up by the plant and so the crop that the gardener will eat. Ideally human waste should have its own composting pile, as it takes longer to break down to a safe form than other waste, such as scraps from the kitchen, and should be left without human contact until fully composted, to avoid the risk of contamination by pathogens before they are broken down. However, if you don’t have a need for compost in the immediate future, you can compost all your waste together; just maintain good hygiene standards when adding kitchen waste to the pile. The feces needs a bulking agent that contains air gaps that allow the functioning of aerobic bacteria to break down the waste. Sawdust and straw are good choices, but rice hulls, peat moss and leaf litter can also be used. The toilet paper and the cardboard tubes at the center of the rolls are perfectly fine to add to the compost pile, just try to use organic, sustainable products. As it should be left in isolation, you won’t be turning the pile as you would a conventional one, so do not cover the pile with a plastic sheet, as it needs air to function. Covering the waste with the bulking agent will prevent odors. The compost pile should also be set up on a soil base so organisms for the soil can enter from the bottom. To fully compost human waste takes about six months.
A composting toilet needs ventilation to add oxygen and prevent the build up of odors. Some composting toilets simply have one side open, facing away from other buildings, but you could consider a three quarter-length door with spaces below and beneath, as well as a vent in the roof. If the toilet does begin to smell, keep a box of a bulking agent, such as sawdust, at hand and add to the tank after depositing. This damps down any odors.
On thing that can put people off installing a composting toilet is that it will require endless emptying, but in fact it can be surprising how little actually accumulates. On average a 25-liter container will take 2 adults around 10 weeks to fill. When you empty a container you will need to wash it thoroughly before reuse, to ensure no pathogens are left behind. Use a long-handled brush and rainwater. It’s really no worse than cleaning the kitchen bin, and you can be secure in the knowledge that you are saving water, preventing pollution and creating valuable compost.