considered to be more efficient include drip or trickle irrigation, surge irrigation, and some types of sprinkler systems where the sprinklers are operated near ground level. these types of systems, while more expensive, usually offer greater potential to minimize runoff, drainage and evaporation. any system that is improperly managed can be wasteful, all methods have the potential for high efficiencies under suitable conditions, appropriate irrigation timing and management. some issues that are often insufficiently considered are salinization of groundwater and contaminant accumulation leading to water quality declines. as global populations grow, and as demand for food increases, there are efforts under way to learn how to produce more food with less water, through improvements in irrigation methods and technologies, agricultural water management, crop types, and water monitoring. aquaculture is a small but growing agricultural use of water. freshwater commercial fisheries may also be considered as agricultural uses of water, but have generally been assigned a lower priority than irrigation (see aral sea and pyramid lake). changing landscape for the use of agriculture has a great effect on the flow of fresh water. changes in landscape by the removal of trees and soils changes the flow of fresh water in the local environment and also affects the cycle of fresh water. as a result, more fresh water is stored in the soil which benefits the agriculture. however, since agriculture is the human activity that consumes the most fresh water, this can put a severe strain on local freshwater resources resulting in the destruction of local ecosystems. in australia, over-abstraction of fresh water for intensive irrigation activities has caused 33% of the land area to be at risk of salination. water requirements of different classes of livestock animalaverage / dayrange / day dairy cow76 l (20 us gal)57 to 95 l (15 to 25 us gal) cow-calf pair57 l (15 us gal)8 to 76 l (2 to 20 us gal) yearling cattle38 l (10 us gal)23 to 53 l (6 to 14 us gal) horse38 l (10 us gal)30 to 53 l (8 to 14 us gal) sheep8 l (2 us gal)8 to 11 l (2 to 3 us gal) approximate values of seasonal crop water needs cropcrop water needs mm / total growing period sugar cane 1500–2500 banana1200–2200 citrus 900–1200 potato 500–700 tomato 400–800 barley/oats/wheat450–650 cabbage350–500 onions350–550 pea350–500 irrigation of green spaces and golf courses urban green spaces and golf courses usually require some form of irrigation. golf courses are often targeted as using excessive amounts of water, especially in drier regions. many golf courses utilize either primarily or exclusively treated effluent water, which has little impact on potable water availability. industries a power plant in poland it is estimated that 22% of worldwide water is used in industry. major industrial users include hydroelectric dams, thermoelectric power plants, which use water for cooling, ore and oil refineries, which use water in chemical processes, and manufacturing plants, which use water as a solvent. water withdrawal can be very high for certain industries, but consumption is generally much lower than that of agriculture. water is used in renewable power generation. hydroelectric power derives energy from the force of water flowing downhill, driving a turbine connected to a generator. this hydroelectricity is a low-cost, non-polluting, renewable energy source. significantly, hydroelectric power can also be used for load following unlike most renewable energy sources which are intermittent. ultimately, the energy in a hydroelectric power plant is supplied by the sun. heat from the sun evaporates water, which condenses as rain in higher altitudes and flows downhill. pumped-storage hydroelectric plants also exist, which use grid electricity to pump water uphill when demand is low, and use the stored water to produce electricity when demand is high. hydroelectric power plants generally require the creation of a large artificial lake. evaporation from this lake is higher than evaporation from a river due to the larger surface area exposed to the elements, resulting in much higher water consumption. the process of driving water through the turbine and tunnels or pipes also briefly removes this water from the natural environment, creating water withdrawal. the impact of this withdrawal on wildlife varies greatly depending on the design of the power plant. pressurized water is used in water blasting and water jet cutters. also, very high pressure water guns are used for precise cutting. it works very well, is relatively safe, and is not harmful to the environment. it is also used in the cooling of machinery to prevent overheating, or prevent saw blades from overheating. this is generally a very small source of water consumption relative to other uses. water is also used in many large scale industrial processes, such as thermoelectric power production, oil refining, fertilizer production and other chemical plant use, and natural gas extraction from shale rock. discharge of untreated water from industrial uses is pollution. pollution includes discharged solutes (chemical pollution) and increased water temperature (thermal pollution). industry requires pure water for many applications and utilizes a variety of purification techniques both in water supply and discharge. most of this pure water is generated on site, either from natural freshwater or from municipal grey water. industrial consumption of water is generally much lower than withdrawal, due to laws requiring industrial grey water to be treated and returned to the environment. thermoelectric power plants using cooling towers have high consumption, nearly equal to their withdrawal, as most of the withdrawn water is evaporated as part of the cooling process. the withdrawal, however, is lower than in once-through cooling systems. drinking water and domestic use (households) main article: drinking water drinking water it is estimated that 8% of worldwide water use is for domestic purposes. these include drinking water, bathing, cooking, toilet flushing, cleaning, laundry and gardening. basic domestic water requirements have been estimated by peter gleick at around 50 liters per person per day, excluding water for gardens. drinking water is water that is of sufficiently high quality so that it can be consumed or used without risk of immediate or long term harm. such water is commonly called potable water. in most developed countries, the water supplied to domestic, commerce and industry is all of drinking water standard even though only a very small proportion is actually consumed or used in food preparation. 844 million people still lacked even a basic drinking water service in 2017.: 3 of those, 159 million people worldwide drink water directly from surface water sources, such as lakes and streams.: 3 one in eight people in the world do not have access to safe water. inappropriate use of water may contribute to this problem. the following tables provide some indicators of water use. recommended basic water requirements for human needs (per person) activityminimum, litres / dayrange / day drinking water52–5 sanitation services2020–75 bathing155–70 cooking and kitchen1010–50 environment explicit environment water use is also a very small but growing percentage of total water use. environmental water may include water stored in impoundments and released for environmental purposes (held environmental water), but more often is water retained in waterways through regulatory limits of abstraction. environmental water usage includes watering of natural or artificial wetlands, artificial lakes intended to create wildlife habitat, fish ladders, and water releases from reservoirs timed to help fish spawn, or to restore more natural flow regimes. environmental usage is non-consumptive but may reduce the availability of water for other users at specific times and places. for example, water release from a reservoir to help fish spawn may not be available to farms upstream, and water retained in a river to maintain waterway health would not be available to water abstractors downstream. recreation recreational water use is mostly tied to lakes, dams, rivers or oceans. if a water reservoir is kept fuller than it would otherwise be for recreation, then the water retained could be categorized as recreational usage. examples are anglers, water skiers, nature enthusiasts and swimmers. recreational usage is usually non-consumptive. however, recreational usage may reduce the availability of water for other users at specific times and places. for example, water retained in a reservoir to allow boating in the late summer is not available to farmers during the spring planting season. water released for whitewater rafting may not be available for hydroelectric generation during the time of peak electrical demand. challenges and threats threats for the availability of water resources include: water scarcity, water pollution, water conflict and climate change. water scarcity this section is an excerpt from water scarcity. water scarcity (closely related to water stress or water crisis) is the lack of fresh water resources to meet the standard water demand. there are two types of water scarcity: physical water scarcity and economic water scarcity.: 560 physical water scarcity is where there is not enough water to meet all demands, including that needed for ecosystems to function. arid areas for example central and west asia, and north africa often suffer from physical water scarcity. on the other hand, economic water scarcity is the result of a lack of investment in infrastructure or technology to draw water from rivers, aquifers, or other water sources, or insufficient human capacity to meet the demand for water.: 560 much of sub-saharan africa has economic water scarcity.: 11 water pollution polluted water this section is an excerpt from water pollution. water pollution (or aquatic pollution) is the contamination of water bodies, usually as a result of human activities, so that it negatively affects its uses.: 6 water bodies include lakes, rivers, oceans, aquifers, reservoirs and groundwater. water pollution results when contaminants mix with these water bodies. contaminants can come from one of four main sources: sewage discharges, industrial activities, agricultural activities, and urban runoff including stormwater. water pollution is either surface water pollution or groundwater pollution. this form of pollution can lead to many problems, such as the degradation of aquatic ecosystems or spreading water-borne diseases when people use polluted water for drinking or irrigation. another problem is that water pollution reduces the ecosystem services (such as providing drinking water) that the water resource would otherwise provide. water conflict this section is an excerpt from water conflict. ethiopia's move to fill the dam's reservoir could reduce nile flows by as much as 25% and devastate egyptian farmlands.water conflict is a term describing a conflict between countries, states, or groups over the rights to access water resources. the united nations recognizes that water disputes result from opposing interests of water users, public or private. a wide range of water conflicts appear throughout history, though rarely are traditional wars waged over water alone. instead, water has long been a source of tension and one of the causes for conflicts. water conflicts arise for several reasons, including territorial disputes, a fight for resources, and strategic advantage. climate change this section is an excerpt from water security § climate change. water-related impacts from climate change affect people's water security on a daily basis. they include more frequent and intense heavy precipitation. another example is faster melting of glaciers. changes in frequency, size and timing of floods are another example. more frequent and severe droughts in some places are another impact. a decline in groundwater storage, and reduction in groundwater recharge are further impacts. and a deterioration in water quality due to extreme events can also be an impact.: 558 climate change affects water resources in various ways. the total amount of freshwater that is available can change, for instance due to dry spells or droughts. the water quality might also get worse due to the effects of climate change. water resource management water resource management is the activity of planning, developing, distributing and managing the optimum use of water resources. it is an aspect of water cycle management. the field of water resources management will have to continue to adapt to the current and future issues facing the allocation of water. with the growing uncertainties of global climate change and the long-term impacts of past management actions, this decision-making will be even more difficult. it is likely that ongoing climate change will lead to situations that have not been encountered. as a result, alternative management strategies, including participatory approaches and adaptive capacity are increasingly being used to strengthen water decision-making. ideally, water resource management planning has regard to all the competing demands for