Infinity pool in a resort in Mauritius Infinity pools are very expensive and require extensive structural, mechanical, and architectural detailing.[citation needed] Since they are often built in precarious locations, sound structural engineering is paramount. The high cost of these pools often arises from the elaborate foundation systems that anchor them to hillsides.[citation needed] The "infinite" edge of the pool terminates at a weir that is 1⁄16 to 1⁄4 inch (2 to 6 mm) lower than the required pool water level. A trough or catch basin is constructed below the weir. The water spills into the catch basin, from where it is pumped back into the pool.