4 Reducing demand
Water, at an average cost to the consumer in England and Wales in 2004 of £0.80 per m3 (0.08p per litre) for supply, has always been cheap compared with other familiar liquids such as milk, petrol or bottled water (all about 60-90p per litre). If you used tap water at the average rate of 150 litres a day and had a pint of milk a day, the annual cost would be about £37 for your water but around £110 for your milk (2004). As well as being cheap, water is also convenient (the only liquid piped to most homes) and there is usually no limit on its use. Not all countries use as much water per head as the UK; in countries where the rainfall is less or is seasonal, water will be either more expensive or rationed unless the country is prosperous, and in extreme cases water is available in such limited quantities that shortage of water is a major factor limiting the economic growth of a country.
People in England and Wales began to be more aware of water supply problems in the 1970s, when water authorities began to collect water rates separately from general rates; this made the domestic consumer really aware of the cost of water for the first time. The point that water supplies are not unlimited was made forcibly by the 1975-76 drought, when rationing by standpipes and cutoff periods had to be introduced in England and Wales (Box 3).
Box 3 Drought in England and Wales
A drought is when there is insufficient rainfall to maintain adequate water levels in rivers, reservoirs and aquifers. This places stress on water resources and the environment. England and Wales had droughts in 1975-76, 1984, 1988-92, and 1995-97.
Figure 5 shows the annual precipitation in England and Wales for 1766-2003. This varies between extremes of about 600 mm and about 1300 mm. There are also longer term drier periods (e.g. 1895-1907) and wetter periods (e.g. the 1870s).
Is low annual precipitation the cause of droughts? Table 4 gives the annual precipitation in England and Wales for 1990-2002. The 1990 and 1991 precipitation values are less than the long-term average and so are the values for 1995, 1996 and 1997. These years of low precipitation are the same as the drought years noted above, so there is a relationship. But drought also depends on temperature, time of year and the water sources used for supply in a particular area.
Table 4 Annual precipitation for 1990-2002 in England and Wales, in mm, and as a percentage of the long-term average (LTA) of 1961-1990 (895 mm). (DEFRA, 2004)
Figure 6 gives rainfall plotted against temperature in England and Wales, for winter and summer periods. The plots for the more recent years, 1974-2003, show a tendency for warmer, wetter winters and hotter, drier summers in comparison with earlier times.
What are the characteristics of 1995 on Figure 6?
1995 has the equal lowest summer rainfall (150mm less than the mean), but a high winter precipitation (170mm higher than the mean). However, it is 2 °C warmer in both summer and winter.
Times of low summer rainfall and high temperatures can produce 'summer droughts' which hit areas mainly supplied from surface water sources. This occurred in 1984, 1989 and 1995. A succession of winters with low precipitation, and reduced aquifer recharge, will produce longer-term drought as in 1988-92 and 1995-97.
Do river discharge and groundwater level data also indicate past droughts? The River South Tyne (Figure 7) had discharges lower than the mean for most months between the spring of 1995 and the autumn of 1997. These were drought years, so there can be a relationship between discharge and drought.
Groundwater level can also be a drought indicator. Figure 8 gives the groundwater level for a well in Norfolk. The low summer rainfall in 1995 caused the water table to fall. Most of the rain in the following winter was absorbed by the moisture-deficient soil, and very little infiltrated to recharge the underlying aquifers. 1996 and 1997 continued to have a low rainfall (Table 4) and it was not until the higher than average rainfall of 1998 that the water table rose to normal levels. However, it is worth remembering that because of the very large volume of water stored in aquifers, groundwater is resilient to droughts in comparison with surface water. The problem is that there are not enough wells to extract the water and those that are available are often overpumped in droughts and may fail. Over-extracting groundwater may also reduce baseflow to rivers.