Sarah Bell, UCL

Managing competing demands for water from a growing and urbanising population is a significant challenge for governments, engineers and citizens. Climate change is likely to make this more complex, as underlying rainfall patterns shift and extreme conditions of drought and flooding become more frequent in some places.

The first plank of any water policy should be to manage demand. The World Health Organisation estimates that each person needs around 50-100 litres of water per day to lead a decent, healthy life. Average domestic per capita daily consumption is UK approximately 150 litres and in the US it is more than 400 litres. Basic water efficiency measures like fixing leaks, installing low flow shower heads and toilets, and encouraging simple changes in daily behaviour like taking shorter showers, help to reduce demand. In agriculture improving the efficiency of irrigation or changing to crops that require less water reduces agricultural demand for water, allowing water to be used for other purposes.

Water pricing and trading have a complex relationship with demand and resources management. Water trading has been used in Australia, Chile and the US to manage water resources for agriculture, cities and the environment. For domestic users, water metering and pricing must balance basic needs and human rights to water with encouraging conservation. Increasing domestic water prices can have considerable negative impacts on people on low incomes, without having a strong influence on the demand from the higher water using people on high incomes. The Right to Water is recognised in the Constitution of the Republic of South Africa, with households on low incomes provided with ‘free basic water’ of 5 cubic metres of water for free each month.

The next option for water policy is recycling and reuse. Most developed countries currently use clean drinking water for everything, including toilet flushing. Rainwater collected from roofs or greywater recycled from washing machines, bath-tubs and showers can be reused for toilet flushing, garden watering and fire suppression. Systems for alternative water supply can operate within individual buildings or neighbourhood scale. Developments in Australia such as Pimpama Coomera have ‘purple pipe’ networks, with houses receiving two different types of water – potable water for drinking and cooking and non-potable recycled water for other uses. Systems like this were installed as a response to drought and population growth, but are being phased out due to high operating costs. In Israel, 74% of municipal wastewater is recycled for to irrigate crops. At the city scale, highly treated wastewater can be recycled through the drinking water. Singapore’s water supply system includes 30% recycled water, and schemes in Wichita Falls and Big Spring in Texas have been recently approved in response to severe drought.

The final option for sustainable water policy is to consider new sources of water supply. Desalination is seen by some as the ultimate technological solution to water scarcity, but it is very expensive and energy intensive. Desalination plants built in Spain, Australia and the US have never been used as they are too expensive to operate. Constructing new dams and reservoirs may be appropriate in underdeveloped catchments and to manage seasonal water flows, but can lead to land use conflict and rely on rainfall that is increasingly uncertain. Transferring water using pipelines requires a lot of energy for pumping, and can extend conflicts over water use and the environment to other regions.

At any stage in water management decision making there are tradeoffs between cost, acceptability, stakeholder needs, energy requirements, environmental impacts and uncertainty. Desalination may provide reliable supply, but it is very expensive, energy intensive and can have significant local environmental impacts. Encouraging domestic water efficiency is low cost, but relies on compliance from millions of water users. Dual supply systems relieve pressure on water resources but require energy for treatment and pumping, and installing a new water distribution network is costly. Domestic rainwater harvesting systems can provide a local source of non-potable water, but pumping and storage of water in individual houses can consume more energy than a municipal supply network.

There is no perfect water policy. Water supply is a major achievement of modern society, but it is becoming increasingly difficult to sustain. Water policy and resource management involve complex trade-offs that are beyond the scope of engineering. Sensible water policy implements measures to reduce supply, and engages citizens and stakeholders in decisions about new supplies. Water policy must meet the needs of local people within the constraints of their local environment, requiring wise and open deliberation about technologies, costs, benefits, risks and the role of water in modern society and everyday life.



Jeremy Bird, Director General of the International Water Management Institute, Colombo, Sri Lanka

The world’s population continues to grow. Today it is 7.5 billion people. That is projected to increase to 8.5 billion in 2030 and 9.6 billion in 2050. And those numbers are deceiving. The population of developed regions will remain largely unchanged from now until 2050. But the 49 least developed countries are projected to double in size from around 900 million people in 2013 to 1.8 billion in 2050. Associated with this comes rapid urbanization and dietary change.

To feed these people we will need to grow as much food in the next 40 years as we have done in the past 8,000 years (see here). But growing food needs large volumes of water. Globally, agriculture is already the largest user of water taking 70% of the total water withdrawn from natural sources. And it is under increasing competition from other sectors of the economy – for example, industry and energy. UN Water notes that about 15,000 litres of water are needed to produce 1 kg of beef. A kilogram of rice grown conventionally requires about 3,500 litres. So where is all this extra water coming from? Or do we actually need more water at all?

On average, around the world there is enough freshwater available for even our future needs. It is just not distributed equally. For example, overall, West Africa as a region has abundant supplies of groundwater, even though large areas are dry and bare. And less than 5% of the water that recharges the Volta Basin is withdrawn.

Ask any farmer what they most want and they will often answer, “reliable irrigation.” Irrigation allows farmers to produce double or triple the yield of rain-fed crops. It also provides a buffer against the increasing variability of rainfall due to climate change where extended dry periods are becoming more frequent even during what was traditionally the wet season. In arid regions it is impossible to grow high value crops without irrigation. Yet in Africa, just 5% of agricultural land is actually irrigated meaning that considerable potential still exists. In the Sahel region, political leaders in 2013 committed to more than doubling the existing irrigated area by 2020.

We cannot increase the amount of water in the system, but we can manage water resources to use them most effectively, and so break the vicious cycle of too much or too little water. For example, storing water in surface reservoirs has long been an option, but techniques for capturing and storing floodwaters underground with lower external impacts is growing. It has the potential to boost groundwater supplies for agriculture, provide irrigation for crops during the dry season and attenuate flooding. Reusing wastewater safely for irrigation is also an increasing reality particularly at the urban-rural interface.

Improving the efficiency of water use in agriculture can also lead to higher agricultural productivity while reducing the amount of water withdrawn. We need to invest more in a whole range of water-storage techniques such as improving the management of moisture in the soil, recharging aquifers as well as storing water above ground. Underground solutions add to conventional approaches of harvesting more water in field ponds, small reservoirs and large dams to deliver context specific solutions for improving resilience by bridging dry spells and increasing the opportunity for dry season agricultural production. Each approach raises different questions on suitability, scale and sustainability. In the past 10-20 years, significant advances have been made in addressing these, in reducing the likelihood of unintended impacts on the environment and society and in ensuring a fairer distribution of benefits.

Making rain-fed agriculture more resilient and managing climate-induced water variability through supplementary irrigation will have a significant impact on food security and livelihoods. Adopting more efficient new irrigation technologies such as drip and sprinkler irrigation in existing schemes plus high-yielding varieties and better agronomic and soil management practices will not only produce more food per unit of water, but also increase the total yield. However what is ‘lost’ water to one farmer may be a gain to a farmer downstream and so we need to be sure that that these are real savings and manage on the basis of water accounts at basin level.

To promote all of these actions, governments will require a mix of new policies and economic incentives. We are aware of the policy implementation gap in many countries and so the use of economic and financial mechanisms to change behavior becomes increasingly important. As development pressures increase and the consequences of current management practice becomes more evident, countries are looking more closely at water management issues across borders. There are semi-arid and dryland areas where the water security challenge is acute and although examples of highly water efficient agriculture exist for such environments, they are not yet been adapted to be relevant for the prevailing economic, institutional and management capacity in many of these countries. 

Over 2 billion people worldwide depend on groundwater from 300 transboundary aquifer systems. About 40 per cent of the world’s population lives in river and lake basins that include two or more countries. As rainfall and river flows become more unpredictable, more attention will need to be given to how nations share the resources, how they deal with the increasing variability and how to reduce risks associated with deteriorating water quality, which in turn compromises the availability of water for productive purposes.

Only by working together will these context specific water challenges be matched with the appropriate solutions.