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A water-flushed toilet depends on water to flush urine and fecal material from a toilet bowl either directly into a pit or more typically through a pipe to a pit, septic tank or sewer. All conventional designs include a trap which forms a water seal. The water may be provided from a cistern or poured from a bucket or other hand-held receptacle.

When water is available on or close to the plot so that per capita water use is at least 25 liters per person per day. Cistern-flush toilets, which use a tank holding 5 to 20 liters of water for flushing, should not be adopted where water availability is less than 60 lpcd. Connections of water flush toilets to sewers also require a reliable water supply offering at least 60 lpcd.

Advantages

Water-flushed toilets are easy to use and keep clean; they are highly popular, and they remove fecal material from the household environment. The water seal prevents flies and smells from entering the house through the waste pipe.

Disadvantages

Water-flushed toilets can produce substantial quantities of heavily contaminated wastewater which can require substantial downstream infrastructure to avoid severe environmental and public health problems. Untreated wastewater can pose dangers to health if the outflow from leach pits may pollute the groundwater table or, even more critically, may be used without treatment for irrigating crops.

Technical requirements

Water flushed toilets require a bowl or pan (into which excreta are deposited), and a water seal created by placing a ‘U’ bend beneath the bowl. The bowl and ‘U’ bend can be integral or can be manufactured separately. The bowl may be designed to allow the user to squat or to sit, according to local custom. Most commercial toilets are manufactured from ceramic or strong plastic materials. Some low-cost designs use cement mortar. Feces will tend to hang to the sides of cement mortar bowls unless they have a very smooth ‘mosaic’ finish. Conventional toilets use a 50mm deep water seal. To reduce the amount of flush water required, some designs reduce this to around 25mm.

Options for wastewater disposal

Wastewater from water-flushed toilets may be discharged either locally to a leach pit, a septic tank and soak away, or to a sewer or drain which carries it away from the plot.