Water Quality Control Purposes | Water Quality | Water Engineering

In this article we will discuss about the water quality control for swimming pools and industrial supplies.

Water Quality Control for Swimming Pools:

Swimming or bathing pools can be divided into the following three categories:

1. Natural Bathing Pools.

2. Partly Natural and partly artificial bathing pools.

3. Artificial bathing pools.

1. Natural bathing pools are usually found on rivers, ponds, etc. and in sometime the quality of water of such pools, is found satisfactory due to an adequate flow of fresh water. But in most of the cases, the water is found polluted and unsafe for bathing purpose.

2. Partly natural and partly artificial bathing pools are constructed at sea side to take advantage of each tide. The location of such pools is decided by keeping the points into mind; the direction of sea currents and the quality of water. If there are chances of pollution of water due to discharge of sewage in vicinity, treatment plant should be installed.

3. Artificial bathing pools are generally constructed by private clubs, or public bodies at various pockets of a modern town or city.

Essential requirements of swimming pool waters and its surroundings:

(i) The water should be clear, of good colour, clarity and attractive appearance.

(ii) It should have approved quantities of disinfectant dissolved in it.

(iii) It should have a comfortable temperature of about 27 °C to 30 °C.

(iv) It should be chemically balanced, as not to cause discomfort and adverse effects on the eyes, nose, throat and skin of men, women and children taking bath in the pool.

(v) Minimum amount of chemicals should be added in treating waters of the swimming pools.

(vi) The water of the pool should be transparent, as to make the pool bottom clearly visible at maximum depth.

(vii) The pool bottom, side walls and surroundings must be maintained clean and hygienic to a very high standard.

(viii) The pool must have an efficient surface water removal system and suitable turn over period for changing the water of the pool.

(ix) The pool hall should also have a pleasant environment with an efficient ventilation system, so as to,

(a) Maintain flow of fresh air without draughts,

(b) Control humidity and prevent condensation of water vapour, and

(c) Remove chlorine effects to avoid coughing and irritation of eyes and nose.

Characteristics of Water to be Used in Swimming Pools:

(a) Hardness:

It is recommended that water to be used in swimming pools must have a minimum hardness of 50 mg/1 (as Ca CO₃) and an ideal hardness of 125 mg/1 (as Ca CO₃). If the hardness of pool water is less than 50 mg/1, it will make the water aggressive, causing erosion and pitting of the tiles and grouting existing on the pool bottom and sides. On the other hand, if the hardness is too high, then scaling will occur and iron present in water may also cause corrosion in filter plant.

(b) pH Value:

The permissible pH range in a swimming pool water is between 7.2 to 8.0 and the preferred range is between 7.4 to 7.6. In order to maintain the pH value to be between 7.4 to 7.6 it usually becomes necessary to add alkalies like sodium carbonate and sodium bicarbonate to increase the pH value, since the pH value in a pool usually decrease due to use of chlorine gas as disinfectant.

(c) Alkalinity:

The alkalinity to be maintained in a swimming pool water will be chiefly governed by the chlorination method being adopted in the pool as indicated in the table.

(d) Total Dissolved Solids:

The permissible T.D.S. in a swimming pool water is 500 – 1000 mg/l. The upper limit is 1500 mg/l, beyond which appearance of water become dull and water may give salty taste and unpleasant bathing conditions.

Control over TDS can be obtained as follows:

(i) Add minimum quantities of chemicals to produce efficient disinfection of the water.

(ii) Back wash the filters regularly with sufficient water.

(iii) Dilute the pool water by adding fresh water from the supply mains to replace some quantity of recycled water.

Chlorination of Swimming Pools:

Chlorine is usually added to the swimming pool water to causes disinfection and helps in removing the bacterial load. Besides killing the germs, it also helps in removing the urine and other nitrogenous pollutants breaking them down into ammonium compounds, which react with chlorine to from chloramines which are soluble in waters.

Since the bathers continuously bacteria and nitrogenous matter (urine) in the pool water, it becomes necessary to add chlorine continuously to the pool water in proportionate amount to ensure free residual chlorine of about 1-2 mg/l, all the time.

Water Quality Standards for Industrial Supplies:

The quality of water required for industries, depends upon the requirements of a particular industry. But in general, about 80% industrial waters are used for cooling and need not be of high quality. The dissolved solids in cooling water may, therefore, range from only few mg/l to 3500 mg/l or so.

It need not, also be free from pollutants either organic or inorganic. It is however, essential to remove the growth of bacteria and other m.o., So as to reduce the fouling of the cooling equipment. Such waters may also sometimes be treated and pH kept not less than 7, so as to prevent or reduce the corrosion.

Boiler Feed Waters:

The water required processing for boiler feed purposes must be of very high quality. The boiler feed waters required for raising steam must be soft, because the hard water will cause incrustation on the inside of the boilers, offering resistance to heat transfer and thus reducing their efficiency. Hand water also cause foaming and priming, and therefore, the boilers using hard waters do require frequency cleaning and addition of chemicals for treating the hard water.

The water required for high pressure boilers (pressure exceeding 70 kg/cm² or so) should contain very low amounts of dissolved solids (of the order of 0.5 mg/l or so) and dissolved oxygen (preferably less than 0.05 mg/l). Since such high standards can never be met in raw available waters or in public supplies fit for drinking, hence special suitable treatments are required, which must be given by the industries themselves.