8. Water conservation and water saving practices and management
8.4. Water savings in domestic applications
Domestic water use can be classified under indoor and outdoor uses. In a typical household having outdoor facilities, nearly 50 % of the water use is for the garden (Stanger, 2000).
Water uses in commercial and services buildings are considered herein together with the domestic ones since they are similar, they are very often located in the same neighbourhood or distribution sector, and water saving measures are common. Also common are water uses for hotels and restaurants. A summary of water savings in domestic uses is given in Table 8.6.
8.4.1. Indoor water uses and savings
A few years ago, as much as 35% of indoors water use could be accounted for by toilets, 30%
by showers, and 20% by clothes washing (Arreguín, 1994). Nowadays, there is a slight change: 33 % concern showers and bath, 24 % are relative to toilet flushing and 22 % to laundry water use (Stanger, 2000). The main attention must be given to the following types of water uses:
(a) Toilets: Traditional toilets use 16 to 20 litres per flush, which means an average of 80 to 100 litres per day per capita. Leaks from the toilet reservoir are the most common system losses in domestic water use, occurring in 15 % of cases as reported in Table 8.5. Water saving in toilets may be achieved by using several means such as:
1. toilets with a reduced reservoir, such as 6 litres per flush,
2. toilets with double discharge, one producing larger flushes, the other a smaller flush, 3. placing containers or bags filled with water in the tank of traditional large volume
toilets to reduce its capacity; however, the toilet’s siphoning effect may be reduced.
4. changing to longer discharge siphons in traditional toilets, which reduces water flushes,
5. toilets having flushes controlled by the pressure in the mains or a pressure regulation device, so that volumes of water discharged may be near 6 litres per flush.
6. special toilets such as with pressurised tanks having the feed line connected to a hermetically sealed tank, so that the pressure within the tank equals the difference in levels between the free surface of the main water tank and the surface of the toilet tank, or biological toilets or incinerators, which degrade faecal matter in deposits located below and turn it into fertiliser.
7. toilets where leaks are easy to detect and repair or toilets less susceptible to leaks such as pressurised tanks without the conventional fittings, and models that substitute siphons for new design fittings.
(b) Showers and bathing Showers take second place in domestic water demand. Water savings include:
1. using shower-head designs that limit the discharge to not exceed fixed values such as 10 l/min,
2. using flow or pressure limiting devices to reduce shower discharges to target values, 3. reducing the time for showering,
4. preferring shower to immersion bathing,
5. controlling leaks in shower fixtures, such as those caused by worn gaskets or loose nuts, which are simple to repair.
TABLE 8.6. Water savings in domestic water uses
Water uses Techniques Applicability
Indoors
Toilets Use reduced flush
Use leak proof fixtures Easy, affordable
costs
Showers Use reduced discharges
Shortening shower duration Easy but needs
willingness Basin taps Reduce pressure and discharge
Use valves for automatic closing
Keep closed when not directly in use
Dish wash in a basin, not in flowing water
Easy but needs care
Cloth washers Use when full
Use washers with less water requirement
Easy Dish washers Use when full
Use washers with less water requirement
Easy Outdoors
Gardens and lawns Irrigate to refill the top 15 cm of soil
Adopt information or tools to decide the irrigation frequency
Select an irrigation method that helps to adopt reduced and localised watering, such as drippers and microsprayers
Irrigate by night, out of the high demand hours and when evaporation is minimal
Under restrictions reduce irrigation frequency, reduce volumes to annuals and lawns but keep irrigating trees and shrubs
Use mulches to avoid soil evaporation
Control weeds
Avoid plants from humid climates
Select native and xerophyte plants
Costs are affordable
washing washing with a hose is water wasteful
dry clean side-walks
use recycling in car wash services
Needs public awareness Swimming pools use water purification tools
cover for evaporation control
Affordable costs General issues
Leak control apply good quality materials and construction techniques
detect and repair
Expensive but effective Pressure control use pressure regulators to avoid excessive
discharges When pressure is
excessive
(c) Basin taps: several water saving measures may be applied in water use from taps in bath rooms and kitchens:
1. flow reduction by using aerators, which add air to the stream and disperse it, increasing the spread and the washing efficiency, reducing flow as much as 6 %, 2. flow reduction by using pressure control devices when the pressure is too high, 3. in hand washing basins, use of valves with sensors that activate the water flow only
when the hands are placed beneath them, or use of valves for limited flow time in
hand washing basins, caring about keeping taps closed when not being required, such as keeping them closed while soaping the hands and opening again to wash, or wash teeth using a glass of water, not flowing water,
4. use of tap valves easy to close and re-open that make it easier to have water flowing only when it is necessary,
5. dish washing in a basin, not with flowing water,
6. controlling leaks in tap fixtures such as caused by worn gaskets or loose nuts.
(d) Washing machines: Water savings in these machines can be achieved by:
1. loading the washers with the appropriate weight of clothes, using the water levels necessary for efficient operation; some modern machines may require less water when half charged,
2. using washers that require less water; front loading washers can use up to half the amount of water (up to 50 % of the hot water and 33 % of the detergent) required by tub or top loading washers; modern washing machines have reduced water use, by up to 25 % in comparison with traditional models,
3. follow instructions of the manufacturer on selecting the programmes since they may have different water and energy demands.
(e) Dish washers: Water savings concern:
1. selection of the machines that require less volume of water to perform the same operations; some modern machines use about one third that of old models.
2. load the machines to full capacity; modern dishwashers have somewhat reduced demand when half charged,
3. follow instructions of the manufacturer on selecting the programmes since they may have different water and energy demands.
(f) Control of indoor leaks: Leaks in pipes, plumbing fixtures and toilets are very frequent and may be difficult to detect. One way to solve the problem is to use leak-proof fittings and other materials whose specifications correspond to pressures to be used as well as to the temperature of the water. Hot water pipes and plumbing often leak. After installation of the pipes, a test must be performed to check joints and valves before walls are closed.
Safety valves must be installed for easy repair operations.
8.4.2. Water savings in outdoor applications
(a) Lawns and gardens: Water saving practices listed under subheading 8.5.(a) can be easily adopted for house gardens and lawns. These concern irrigation methods and scheduling, and irrigation practices when restrictions in water supply are enforced.
The conversion from turfgrass to xeriscape (low water-use landscape) in house gardens has been studied in Nevada, USA, where typically 60 to 90 % of potable water drawn by households is used for outdoor irrigation. A xeriscape is characterised by sound landscape planning and design, limited use of turf, use of water-efficient plants, efficient irrigation, soil amendments and mulches, and proper landscape maintenance procedures. The study, concerning 499 properties, shows that the adoption of xeriscape reduced the water use for outdoor irrigation by 33 % relative to a turf landscape, that proportion being 39 % during the summer months (Sovocool and Rosales, 2001). This may represent an enormous saving of good quality municipal water for areas of hot, dry extreme climates.
(b) Sidewalks: should be cleaned dry. To wash stone or concrete sidewalks with a flexible hose is water wasteful.
(c) Swimming pools:
1. water used to fill a swimming pool can be continuously recycled, clarified and purified by using easy to handle portable equipment and appropriate chemicals. It may be then renovated after one year or so,
2. leakage losses may be prevented using appropriate construction materials and techniques. When empty it is advisable to check the state of the sides and bottom and perform the appurtenant repair if necessary,
3. evaporation losses can be minimised by covering the pool when not in use.
(d) Car washing:
1. washing cars with a hose is water wasteful. It is recommended that just a bucket and cloth be used.
2. car wash services should recycle or reuse water.
Most of the fixtures discussed above, both indoors and outdoors increase their rate of discharge in direct proportion to the water pressure. In areas where pressure is high, the use of pressure-reduction valves is recommended.