2 Water abstraction and its uses
The quantities of fresh water abstracted for various purposes in England and Wales are given in Table 1. Water is abstracted under licences from the EA, issued on the basis of the reasonable needs of the public, industry and agriculture and availability of supplies.
Table 1 The quantities of fresh water (non-tidal surface water and groundwater) abstracted for different uses in England and Wales in 2001. (DEFRA, 2004)
|Water use||Quantity/106 m3 per day|
|public water supply||16.23|
|electricity supply industry||18.07|
|agriculture (includes irrigation and fish farming)||4.66|
Calculate the total water abstracted in litres per person per day in England and Wales for 2001. Take the population as 50 million.
The total amount of water abstracted in 2001 (Table 1) was:
- 43.11 × 106 m3 per day
Quantity per person per day = (43.11 × 106/50 × 106)m3
- = 0.86m3 or 860 litres
The public water supply is the water abstracted, purified and distributed through water mains to houses, offices, some industries and farms by the water companies. The other types of users given in Table 1 get much of their water directly from rivers or the ground without going through the treatment works and distribution system of the public water supply. Industry, power stations and farms often do not require high-quality water, so it is cheaper to abstract water directly than to use the more expensive, high-quality public water supply. In England and Wales the direct abstraction of water is permitted only where it is licensed by the EA, which has to ensure that there is enough water available and that it will not affect other abstractions. For example, if an industry or power station takes water directly from a river, the EA has to make sure that there is still enough water in the river at all times, and will license abstraction only up to a certain quantity. Direct abstraction is not restricted to industry: in principle there is nothing to stop you digging a well in your garden for your own domestic water supply.
As Table 1 shows, the largest use of water is for electricity generation. Because of the enormous quantities of water required, power stations are situated on major rivers, lakes or on the coast. The main use of water is for cooling, and this water can be of low quality. Even more water is obtained from estuaries (brackish water) and the sea (saline water). The water used for cooling is returned to its source relatively quickly but some 5 °C warmer. There are considerable year-to-year fluctuations in the amount of water used for electricity generation. Some power stations recycle cooling water; this is not a continuous yearly demand but is a 'one-off' abstraction that stays within the cooling systems and is never returned.
Another use of water in electricity generation is for raising steam in boilers, to convert thermal energy first into mechanical and then into electrical energy. Boilers require high-quality water, but only in relatively small amounts.
Direct abstraction by industry generally reduced during the 1980s, falling by 42% between 1980 and 1988. It increased slightly after 1998. The main causes for the reduction were the more efficient use of water, including recycling, and changes in the structure of British industry, including the contraction of some of the major water-using industries, such as steel-making.
Agriculture consumes only a small proportion of the total water abstracted (Table 1), although, on a global scale, irrigation is the greatest use of water. There is sufficient rainfall for agriculture over Wales and the western and northern parts of England so irrigation is used mainly in the drier central, southern and eastern parts of England, particularly in East Anglia (Figure 1). Irrigation water is usually obtained by direct abstraction from rivers and boreholes and it can be of low quality.
A significant and increasing proportion of the UK's root and vegetable harvest is produced using irrigation; for example 36% of the UK potato crop is currently (2004) irrigated. The amount of water abstracted for irrigation is greater in dry summers, and there is also a long-term increase. The installation of irrigation equipment is increasing, partly in response to supermarket demand for a consistent high quality product, but also in response to the more frequent occurrence of dry growing seasons in recent years. Although the quantity used for irrigation is relatively small in total, it tends to be highest in hot dry weather when water resources are most stretched. Also most of the irrigation water is lost to the atmosphere, whereas water used for most other purposes is eventually returned to rivers and can be reused.
In England and Wales, an average of 150 litres of water per person per day is used in the home (in comparison with the average of 860 litres per person per day for domestic, industrial and agricultural purposes in industrialised countries calculated in Activity 1). The domestic demand has grown from 36 litres per person per day at about the time of the last major cholera epidemic in London (1858) to 150 litres today because of improved living standards. Nearly all (over 99%) homes in England and Wales are now linked to the public water supply. Similar patterns of water use exist in other industrialised nations.
In this Activity you will measure how much water you use in one of these two categories, that of a bath or a shower.
Over a period of one week, keep a record of how many baths and/or showers you have, and the duration of each shower. Work out how much water you use in an average bath, by measuring how long your bath tap takes to fill a measuring jug or kettle, and how long the bath takes to run. Do the same for a shower, measuring how long it takes to fill the jug or kettle, so you can calculate the amount of water use per minute of shower.
Calculate your weekly water use for a bath or shower, and finally your daily use averaged over a week.
These are my results for the first week in June; yours will be different, but these might be useful to demonstrate how to go about this Activity.
Number of baths in a week = 1
Number of showers in a week = 5
Time taken by bath tap to fill a 1 litre jug = 3 s
Length of time tap runs to fill a bath = 3 minutes, 10 s = 190 s
Water used per bath = 190/3 litres = 61 litres
Time taken by shower to fill a 1 litre jug = 9 s
Water used per minute of shower = 60/9 litres = 7 litres
Total length of time for five showers = 37 minutes
Total water use for five showers = 7 × 37 litres = 259 litres
Total bath/shower water use per week = 61 + 259 litres = 320 litres
Averaged bath/shower water use per day = 320/7 litres = 46 litres