A sink-toilet combination unit is sometimes used by prisons and militaries.^[1][2] Such units typically have no exposed pipes by which someone could hang himself. They are sometimes made of stainless steel for added durability. Sink-toilets are used at the Guantanamo Bay detention camp.^[3] Sink-toilets are also used in some homes as an environmentally friendly, water-saving option that, at the user's option, reuses waste water from the sink in the discharge of the cistern. Some sink toilets employ a filtration system to remove particles, debris, bacteria, and odors before the water is stored for flushing.