Water Conservation

Subsurface irrigation is an emerging technology with high water-utilization efficiency. Subsurface irrigation uses a drip-irrigation tubing buried 6–8 in (15–20 cm) underground, with a spacing of 12–24 in (30–60 cm) between parallel lines. The tubing contains drip outlets that deliver water and nutrients within the root zone at a desired rate. In addition to water conservation, subsurface irrigation has other advantages that overhead sprinklers do not: minimal over watering, fewer disease and aeration problems, less runoff and erosion, fewer weeds, and better protection from vandalism. However, this system is relatively expensive to install. In California, subsurface irrigation has been used on fruit trees, field crops, and lawns, and has achieved water-use savings of about 50%. However, this methodology can, in arid environments, lead to the buildup of soil salinity levels, damaging plants and reducing crop yields. Balancing the water needs of the plant with maintenance of soil quality is an important component of water conservation measures. Technologically advanced irrigation systems now incorporate climate-based controls. These systems utilize meteorological information to determine the need for irrigation and modify the length and duration of irrigation to match the plant's requirements. Though these systems are currently used primarily on large-scale applications, development of economical models for the small-scale user is underway.

Xeriscaping, or the cultivation of plants requiring little water, is an especially suitable horticultural practice for conserving water in regions with a dry, hot climate. For example, over much of the southwestern United States, more than 50% of the domestic water consumption may be used to irrigate lawns and other horticultural plants that are intolerant of drought. Xeriscaping uses plants such as cacti, succulents, and shrubs of semi-desert habitat (such as trailing rosemary Rosemarinus officinale and rock rose Cistus cobariensis), which are well-adapted to a hot, dry climate and need little water.

Water conservation can also be advanced by improving other domestic uses of water. One simple conservation practice is to install ultra-low-flush (ULF) toilets and low-flow showerheads in homes and other buildings. A ULF toilet uses only 1.6 gal (6.1 l) per flush, compared to 5–7 gal by a standard toilet. Replacing a standard toilet with an ULF saves about 30–40 gal (114–151 l) of water per day, equivalent to 10,000–16,000 gal (37,850–60,560 l) per year. More recently, advanced toilets and urinals requiring no water have been developed and are beginning to be utilized on a limited basis.

Another way to conserve the freshwater supply is to desalinize seawater. Desalinization is the removal of salts and other impurities from seawater by either distillation or reverse osmosis (RO), and this method being increasingly used to provide high-quality water for drinking, cooking, and other domestic uses. In 1993, the world production of desalinated water was about 3.5 billion gallons per day (13 billion liters), most of which was produced in Saudi Arabia and other nations of the Gulf of Arabia, where energy costs are relatively low (the cost of desalinated water is highly sensitive to the cost of energy). Desalinization is also practiced in California and Florida, where the cost is about three dollars per thousand gallons, which is four to five times the cost paid for domestic water by typical urban consumers in the United States, and more than 100 times the cost paid by farmers for water for irrigation.

Widespread recognition of the importance of reusing water has begun to change traditional water use methods. As the value of water increases, users are willing employ methods that may increase the initial cost of a project, with the hope of regaining those costs through water savings in the future. One of the first of these reuse applications was the irrigation of golf courses and landscaping. In many areas, treated wastewater is diverted from its normal disposal path to be reused in irrigation. This has gained in popularity and is also utilized in small artificial ponds for decorative purposes. Greywater systems capture water that drains from sinks, tubs, laundry, and dishwashers for reuse in irrigation. Greywater systems do not incorporate toilet wastes because of the potential health threat. Dual plumbing is required for such a system and some treatment is required prior to reuse. Though home construction costs are obviously increased by including a greywater system, many have become dedicated believers in the benefits of water reuse, while others question the economic benefit of small-scale systems. The widespread application of greywater systems has, however, been hampered by codes and laws that make such systems illegal in many locations.