Wasting Water

Water is a renewable natural resource, yet limited access to freshwater renders it finite. Irrigation for agriculture is the largest consumptive use of water (Bouwer, 1994). The majority of our freshwater is stored in aquifers as groundwater and is abstracted for irrigation. However over-abstraction can result in aquifers becoming unproductive. Dams are often built to store water in irrigation reservoirs but these alter the natural hydrological cycle.

In 2000 agriculture accounted for ~ 75% of human water use (Wallace, 2000). Availability of fresh water is therefore a major limiting factor in population expansion. As the global population increases the demand for food increases and thus the demand for water increases. However, for the foreseeable future, ‘annual renewable freshwater resources are largely fixed’ therefore with population growth water scarcity becomes a huge concern (Wallace, 2000).

Irrigation is very inefficient, Wallace (2000) states that crops actually only use 10-30% or water put onto the land. Runoff losses and deep percolation are sources of inefficiency (Bouwer, 1994). Pimentel, et al. (1997) point out that controlling erosion can help to conserve water by reducing runoff and protecting forests and other biological resources can help maintain the hydrological cycle. As agriculture intensifies, soil erosion and deforestation are both likely to increase, therefore threatening long-term sustainability of water supplies.

Evapotranspiration is another major source of water loss from agriculture, which is likely to increase with climate change. Bouwer (1994) likens irrigated fields to evaporation pans where water is evaporated and salts are left in the soil, which can reduce the quality of the soil. The only way to reduce this water loss is to reduce the irrigated area while maintaining yields, by increasing crop yield per unit of water used (Bouwer, 1994). We need to increase the production of food for our growing population with the existing supplies of land and water (Wallace, 2000). This means agriculture must become even more intensive and even more reliant on fertilizers and pesticides. This in turn increases pollution of the limited freshwater supplies and can result in eutrophication.

            Water resource management will become increasingly complicated as the population continues to rise, especially as the areas with the largest populations to feed are often the most water scarce areas (Wallace, 2000). Wallace (2000) argues that this problem isn’t given enough attention by the scientific community. He believes that science can be used to develop the ability to grow more food with less water. Pimentel et al (1997) point out that most human activity has a negative effect on the quality of freshwater sources, as population continues to grow this effect will increase and the increased demand for water will become even more difficult to meet.