Compare quality of water from surface and sub-surface sources. Give usefulness for public water supplies.
Quality of Surface Water with its Usefulness –
The rain water which is pure at the upper atmosphere gets considerably polluted till it reaches the river streams. The gases, dusts, etc., from the atmosphere, get added to the rain water till it reaches the ground, from where onward, it flows on earth’s surface and also through drains, channels, etc. which add a lot of organic as well as inorganic impurities to it. Sometimes, sewage and industrial wastes get added to this water, making it highly contaminated.
inorganic impurities such as silt, clay, etc. get added due to erosion from the beds of the stream channels. The organic impurities get added in the form of vegetable washings, dead organic matters, and dead animals, etc.
On the whole, it can be stated that the surface supplies are generally contaminated and cannot be used with minor treatment or without any treatment. They, therefore, need building up of proper purification plants and other connected works before being used for public supplies. They are useful for big cities and large industrial towns where huge quantities of water are required by the public.
Quality of Sub-surface Water with its Usefulness
The underground water supplies are generally purer and safer, because theyater before getting stored in the underground reservoir, undergoes natural filtration during percolation through the soil pores. These waters are generally free from organic , matter and suspended impurities, which is generally responsible for disease producing bacteria. These waters are, therefore, less likely to be contaminated by bacteria. However, they are likely to contain greater amounts of dissolved Salts, minerals, gases, etc. These may impart different tastes, odours and some ether properties, such as, hardness, etc. to it.
Hard rocky soils which do not easily dissolve, therefore, provide better underground water. Although the quality of undergror‘md water is quite safe, yet it is advisable to protect these sources from possible dangers of pollution. Since the chances of outside pollution are much less in an artesian aquifer, the quality of tubewell water, drawing water from the 2nd or even lower water bearing strata, is generally very safe. These waters can be supplied to the public after proper testing, with minor treatment or sometimes even without any treatment.
Underground waters are generally found colder in hot seasons and hotter in cold seasons. They are useful for domestic purposes.