Water supply

UNIT – III

Chapter - 9

WATER SUPPLY AND RAINWATER HARVESTING

 

WATER SUPPLY

The essential requirements for human existence are air, water, food, heat and light. Water is of major importance to all living things; in some organisms, up to 90% of their body weight comes from water. Up to 60% of the human adult body is water. Each day humans must consume a certain amount of water to survive. Of course, this varies according to age and gender, and also by where someone lives. Generally, an adult male needs about 3 liters per day while an adult female needs about 2.2 liters per day. Some of this water is taken from food.

Water supply is the provision of water by public utilities (For Example: Tamilnadu Water Supply and Drainage Board-TWAD), commercial organizations, community endeavour or by individuals, usually through a system of pumps and pipes. Inadequacies in water supply affect health adversely both directly and indirectly. An inadequate water supply also prevents good sanitation and hygiene. Consequently, improvements in various aspects of water supply present opportunities to enhance public health.

 

1. SOURCES OF WATER SUPPLY

In nature, water is available abundantly as:

1. Water vapour in the atmosphere,

2. Liquid water in inland waters and the ocean,

3. Ice in polar regions, and

4. Water of hydration in many rocks and minerals in the earth's crust.

The original source of all natural water supplies is, however, rain. Rain water, in its passage through the air, dissolves many of the soluble gases present in the atmosphere. It also collects mineral salts and other impurities while percolating through the various strata of the earth. These may be either acidic or alkaline.

Of the dissolved gases, oxygen and carbon dioxide are the most important. The dissolved minerals include carbonates, bicarbonates, chlorides, sulphates and nitrates of calcium, magnesium, sodium and sometimes iron also. The water available may also contain suspended matter, both mineral and organic.

1. Rain Water: Rain water is the purest form of water. In order to be absolutely pure, it should be collected after a heavy shower, because prior to that, the water may contain dissolved gases and also dust. In industrial areas, gases in the atmosphere may contaminate rain water. For example, it may result in the formation of sulphuric acid.

Dissolved carbon dioxide renders water acidic and increases its solvent power. When this acidic water passes through the soil, it reacts with the calcium and magnesium carbonates present in the soil and forms bicarbonates. Pure rain water is soft.

2. River Water: River and canal waters are inland waters fed by rains. These are less pure than rain water as they contain dissolved chemicals. Their composition is subject to considerable variation depending on the areas over which they are flowing and the soluble chemical salts present in the rocks and soil. Dissolved solids in the river water also vary with the rate of flow.

The impurities in river water are generally the carbonates, bicarbonates chlorides and sulphates of calcium, magnesium and iron. The soluble bicarbonates of calcium and magnesium are formed by the action of dissolved carbon dioxide upon insoluble carbonates. The presence of soluble calcium and magnesium salts in river water makes it hard. Besides this, river and canal waters are liable to be contaminated with sewage and sludges of cities through which they flow and also organic matter, ammonia and nitrites.

3. Spring and Well Water: This is percolated rain water which, on reaching the ground, passes through the various strata of the soil. It results in dissolving the soluble salts of the soil. This water is extremely clear as a result of natural filtration through sand beds and strata. It contains a much higher percentage of dissolved mineral matter when compared to rain water. It is free from organic impurities and ammonia. It has a palatable taste and may be used for drinking. Water from springs and wells is extremely hard.

4. Surface Water and Ground Water: As rain falls on the earth, it flows into streams as surface runoff, passes into the air as vapour and goes down into the ground. It is then recovered as surface water or ground water.

The term surface water indicates natural water in rivers, streams, ponds and lakes, although a part of water may have percolated through the soil while flowing along the earth's surface. As a result, water absorbs a part of the materials with which it comes in contact. Surface water, therefore, indicates the chemical constitution and physical conditions of the area in which it is available.

The water obtained from springs and wells in a given locality may be very different from the local surface water. Ground water also indicates the local geological strata and contains a greater percentage of dissolved salts. Ground water is nearly constant in composition. Some of the ground water may be hot and may contain dissolved gases. It is sometimes used for medicinal baths. Ground water may be different in taste and chemical character--acid, alkaline, bitter, hepatic, ferruginous, iodineus or siliceous.

5. Sea Water: Rivers carry a large volume of water with dissolved impurities into the sea and, as such, the sea contains the maximum amount of dissolved impurities. The total dissolved impurities in sea water are about 3.6 per cent of which 2.6 per cent is common salt; others are magnesium chloride, magnesium sulphate, calcium sulphate, potassium chloride, magnesium bromide and traces of iodides, silica, etc. The quantity of dissolved salts is very much greater in inland seas. Sea water is saline and hence it is not suitable for drinking purposes. It is hard and also faintly alkaline.

 

2.  QUALITY OF WATER

The quality of water depends entirely upon its source of supply. Water quality is determined by measurements of the characteristics of water, which include chemical, biological, physical, and radiological characteristics. This is usually measured relative to human needs. It is also looked at in terms of how the quality of water affects animal and plant ecosystems. Water quality is measured considering the following aspects:

• A water sample's pH is a measure of how acidic or alkaline the water is. Good quality water should be close to neutral, which is a pH of 7. Numbers bigger than that are alkaline, and numbers smaller than that are acidic. Strong acids are caustic, and strong alkalis are corrosive. Acids burn away at your tissues and cause pain, whereas alkalis get absorbed into tissues. Either way they cause a lot of damage. Neutral water is easier for the body to handle. Water's pH depends on other things being mixed in the water. Slightly alkali water is usually due to minerals and is probably fine.

• Heavy metals are metals that have high densities, and usually refer to toxic heavy metals like cadmium, mercury, arsenic and lead. The above metals could have got into the water due to nearby factories or old lead piping. It is important that water contains as few of them as possible. The human body has to work hard to filter them out and avoid those killing cells.

• Radon is a radioactive element that is bad for humans, and can sometimes be found in water supplies. It happens when water is supplied from underground. Some radioactive material is natural because it is found in many rocks underground. Radon can cause the development of cancers in humans, and so is best avoided.

• Drug content refers to the amount of pharmaceutical drugs found in the water. The presence of drugs is due to factories pumping waste products into the water, and due to farmers giving drugs to their livestock. They have all kinds of mixed effects on humans and hard to predict.

There are other indicators that might be important in terms of the health of non-human ecosystems too, like turbidity (transparency), dissolved oxygen, suspended solids, temperature, and presence of particular kinds of bacteria.

Turbidity and dissolved oxygen are two measures that are particularly important for water-based animals.

• Turbidity is a measure of how clear the water is (i.e) how many particles like sand, silt, clay, algae and others are found in the water. Some animals prefer clearer water, and some are healthier in cloudy water. Humans prefer their water clear, and most governments have rules on how cloudy water can be. Dissolved oxygen enables fish to breathe through their gills. Entire populations of fish can be killed if dissolved oxygen gets too low.

• Dissolved oxygen varies with temperature, water speed and roughness. Water high in oxygen tastes better for human beings. Most human water supplies are low in dissolved oxygen because it damages water pipes over time.