Even without water for flushing, toilet wastes are mostly water. Urine is more than 98% water and faeces are more than 70% water. The actual amount of solid matter we excrete is quite small – less than 50kg a year, compared with around half a tonne with all the water included. It is tempting then, and technically possible, to deal with toilet wastes simply by dehydration, and this is the principal method adopted by some commercial dry toilets. One can go even further and incinerate the resultant dry matter, reducing it to a few kilos of ash. One US model, no longer produced, was called the 'Destroilet'...

Disadvantages:

• an electricity connection is needed
• electricity consumption potentially significant – often the toilet will become the largest-consuming appliance in the house
• they are vulnerable to SHOCK LOADS – there is an upper limit to the rate at which it can accept inputs over a short period
• problems often arise if the unit is not in continual use
• the product may be hygienic when removed, but may not be actually composted and requires further treatment to become stable
• there is a risk of total failure in the event of an extended power-cut

Sometimes such compact electrical toilets are the best and only solution, but in practice users are often dissatisfied. The units are very sensitive to misuse – readily overwhelmed by a serious party, for example. Re-commissioning after a breakdown is not a job for the faint-hearted. A common problem arises when the units are installed in holiday-homes and are left for long periods without use. The de-watering process can sometimes transform a mixture of toilet paper, urine and faeces into a kind of paper mâché that coats the innards of the toilet so tenaciously that it is almost impossible to remove. Its strength is so impressive one imagines there could be industrial applications for it.