LONDON Growing global demand for more and cleaner water is sapping energy, throwing a focus on efficiency for example in world farming sector trying to feed more people, said a study published in the journal Nature.
Concerns have grown about scarcity of food, water and energy as the world tries to feed an extra 2 billion people by 2050.
It is important to understand links between these better, to avoid creating a shortage in one while boosting another, said researchers from Britain's University of East Anglia.
Water demand was growing in agriculture, domestic and industrial sectors, but the knock-on impact on energy and carbon emissions from burning more fossil fuels was poorly understood, said the paper, "Greenhouse-gas emissions from energy use in the water sector".
Energy use is especially high in the agriculture sector, for example to pump groundwater for irrigation -- which accounts for a disproportionate amount of the world's food supply -- as populations rise and climate change sparks droughts.
"The water sector is very energy intensive and also highly sensitive to climate change," the study found in a review of energy consumption and carbon emissions from different types of water use worldwide.
"Very few (studies) have looked at the implications of changing water use for fossil fuel use and CO2 emissions."
"Environmental targets and water-supply strategies tend to be poorly integrated with energy efficiency and climate change policies."
Energy is used both to build water infrastructure, and in extraction, transport and treatment.
Answers to the problem included greater regulation, for example of groundwater wells, more precise, "pressurised" irrigation and use of renewable energy.
R&D investment by water companies in Britain had fallen 60 percent from 1999 levels, the study found. In a useful consumer awareness measure, the U.S.-based Pacific Institute research centre had created a water, energy and carbon emissions calculator for households.
In Britain, higher water quality standards had seen rising energy use by the water industry over the past two decades for transport and treatment.
Studies suggested that the Indian irrigation sector may account for 6 percent of national carbon emissions, and in some regions of India for almost half of all energy demand.
In China, farming consumed more water less efficiently than any other sector, the paper said, in a trend worsened by a regional imbalance where most water was in the south and crops in the north, while a lack of regulation had allowed a proliferation of groundwater wells.
China's net irrigation needs are projected to rise by 2-15 percent by 2020.
Another major demand for energy in water is from the energy sector itself, where energy is used for example to create steam to drive turbines in power plants, and to produce biofuels.