Editing Autonomous building (section)

===Water===
[[File:Ceres rainwater tank 2 Pengo.jpg|thumb|right|A domestic [[rainwater harvesting]] system]]
[[Image:Unterirdische Zisterne.jpg|thumb|right|A concrete under-floor cistern being installed]]

There are many methods of collecting and conserving water. Use reduction is cost-effective.

[[Greywater]] systems reuse drained wash water to flush [[toilet]]s or to water lawns and [[garden]]s. Greywater systems can halve the water use of most residential buildings; however, they require the purchase of a sump, greywater pressurization pump, and secondary [[plumbing]]. Some builders are installing [[waterless urinal]]s and even [[composting toilet]]s that eliminate water usage in sewage disposal.

The classic solution with minimal life-style changes is using a [[water well|well]]. Once [[Drilling|drilled]], a well-foot requires substantial power. However, advanced well-foots can reduce power usage by twofold or more from older models. Well water can be contaminated in some areas. The [[Sono arsenic filter]] eliminates unhealthy [[arsenic]] in well water. However drilling a well is an uncertain activity, with [[aquifer]]s depleted in some areas. It can also be expensive.

In regions with sufficient rainfall, it is often more economical to design a building to use [[rainwater harvesting]], with supplementary water deliveries in a [[drought]]. Rain water makes excellent soft washwater, but needs antibacterial treatment. If used for drinking, mineral supplements or mineralization is necessary.<ref>{{Cite web|url=https://www.who.int/water_sanitation_health/dwq/nutconsensus/en/|archive-url=https://web.archive.org/web/20040912052010/http://www.who.int/water_sanitation_health/dwq/nutconsensus/en/|url-status=dead|archive-date=September 12, 2004|title=WHO &#124; Nutrient minerals in drinking-water and the potential health consequences of consumption of demineralized and remineralized and altered mineral content drinking-water: Consensus of the meeting<!-- Bot generated title -->}}</ref>

Most [[desert]] and [[temperate]] climates get at least {{convert|250|mm|in}} of [[rain]] per year. This means that a typical one-story [[house]] with a greywater system can supply its year-round water needs from its roof alone. In the driest areas, it might require a [[cistern]] of {{convert|30|m3|USgal}}. Many areas average {{convert|13|mm|in}} of rain per week, and these can use a cistern as small as {{convert|10|m3|USgal}}.

In many areas, it is difficult to keep a roof clean enough for drinking.<ref>{{Cite web|url=http://www.uaf.edu/ces/publications/freepubs/HCM-01557.pdf|archive-url=https://web.archive.org/web/20080517155419/http://www.uaf.edu/ces/publications/freepubs/HCM-01557.pdf|url-status=dead|title=Cistern Design, University of Alaska, referenced 2007-12-27|archive-date=May 17, 2008}}</ref> To reduce dirt and bad tastes, systems use a metal collecting-roof and a "roof cleaner" tank that diverts the first 40 liters. Cistern water is usually [[water chlorination|chlorinated]], though [[reverse osmosis]] systems provide even better quality drinking water.

In the classic Roman house ("Domus"), household water was provided from a cistern (the "impluvium"), which was a decorative feature of the atrium, the house's main public space. It was fed by downspout tiles from the inward-facing roof-opening (the "compluvium"). Often water lilies were grown in it to purify the water. Wealthy households often supplemented the rain with a small fountain fed from a city's cistern. The impluvium always had an overflow drain so it could not flood the house.<ref>{{cite web|last1=Becker|first1=Jefferey|title=The Roman House (Domus)|url=https://www.khanacademy.org/humanities/ancient-art-civilizations/roman/beginners-guide-rome/a/roman-domestic-architecture-domus|website=Khan Academy|access-date=13 May 2018}}</ref><ref>{{cite book|author=Vitruvius|translator-last1=Morgan|translator-first1=Morris Hickey|title=The Ten Books of Architecture|date=1914|publisher=Harvard University Press|page=6.3|url=http://academics.triton.edu/faculty/fheitzman/Vitruvius__the_Ten_Books_on_Architecture.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://academics.triton.edu/faculty/fheitzman/Vitruvius__the_Ten_Books_on_Architecture.pdf |archive-date=2022-10-09 |url-status=live|access-date=13 May 2018}}</ref>

Modern cisterns are usually large plastic tanks. Gravity tanks on short towers are reliable, so pump repairs are less urgent. The least expensive bulk cistern is a fenced pond or pool at ground level.

Reducing autonomy reduces the size and expense of cisterns. Many autonomous homes can reduce water use below {{convert|10|USgal|L}} per person per day, so that in a [[drought]] a month of water can be delivered inexpensively via truck. Self-delivery is often possible by installing fabric water tanks that fit the bed of a pick-up truck.

It can be convenient to use the cistern as a heat sink or trap for a [[heat pump]] or [[HVAC|air conditioning]] system; however this can make cold drinking water warm, and in drier years may decrease the efficiency of the HVAC system.

[[Solar still]]s can efficiently produce drinking water from ditch water or cistern water, especially high-efficiency [[multiple effect humidification]] designs, which separate the evaporator(s) and condenser(s).

New technologies, like [[reverse osmosis]] can create unlimited amounts of pure water from polluted water, ocean water, and even from humid air. [[Watermaker]]s are available for yachts that convert seawater and electricity into [[drinking water|potable water]] and [[brine]]. [[Atmospheric water generator]]s extract moisture from dry desert air and filter it to pure water.