For a variety of reasons; if the installation in mind is far from a water source or in an area of low supply, or you simply wish to consume less, the answer is self evident. In a self contained, exterior installation, a waterless toilet will almost certainly be less expensive to install, considering the cost of bringing water to the site and hooking up to the waste water network. In an internal, mixed environment, (e.g., where water is available and used for sinks), waterless toilets can greatly simplify the treatment of the waste water. In all cases, due to the fact that waste is treated on site, a waterless toilet will typically impose less strain on environmental resources.

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