Water Quality

Water Quality

Water quality is determined by assessing three classes of attributes: biological, chemical, and physical. There are standards of water quality set for each of these three classes of attributes. The standards for drinking water are developed by Environmental Protection Agency (EPA), World Health Organization (WHO) etc. All municipal (public) water supplies must be measured against these standards.

Some attributes are considered of primary importance to the quality of drinking water, while others are of secondary importance. Therefore, the drinking water standards are categorized as primary drinking water standards and secondary drinking water standards. Primary drinking water standards regulate organic and inorganic chemicals, microbial pathogens, and radioactive elements that may affect the safety of drinking water. These standards set a limit--the Maximum Contaminant Level (MCL)--on the highest concentrations of certain chemicals allowed in the drinking water supplied by a public water system. Secondary drinking water standards regulate chloride, color, copper, corrosivity, foaming agents, iron, manganese, odor, pH, sulfates, total dissolved solids, and zinc, all of which may affect qualities of drinking water like taste, odor, color, and appearance. The concentration limit of these contaminants is referred to as the Secondary Maximum Contaminant Level (SMCL). State agencies like the Public Health Engineering department (PHED) are responsible for monitoring public water supplies and enforcing the primary and secondary drinking water standards set by the EPA/WHO. Local water organizations must test and treat drinking water and maintain the standards for quality. These districts are also responsible for informing the public when any water quality standards have been violated. Given these standards, stream- and groundwater supplies should be of high quality. Generally, one compares the values for the various measures of stream- and groundwater quality at a given time and location to the average of those values across the entire watershed.

A. Drinking Water Quality Parameters

1. Physico Chemical Parameters

pH: The logarithm of the reciprocal of hydrogen-ion concentration in gram atoms per liter; provides a measure on a scale from 0 to 14 of the acidity or alkalinity of a solution (where 7 is neutral and greater than 7 is basic and less than 7 is acidic). Acidic water results in pipes corrosion whereas basic water results in exceeded ammonia concentration. Measured with pH meter.

Turbidity: The optical property of a water sample that causes light to be scattered and absorbed rather than transmitted in straight lines through the sample. Light’s ability to pass through water depends on how much suspended material is present. Turbidity may be caused when light is blocked by large amounts of silt, microorganisms, plant fibers, sawdust, wood ashes, chemicals and coal dust. Any substance that makes water cloudy will cause turbidity. Hence turbidity indicates the presence of suspended particles in drinking water. The most accurate way to determine water’s turbidity is with an electronic turbidimeter. The turbidimeter has a light source and a photoelectric cell that accurately measures the light scattered by suspended particles in a water sample. The results are reported in units called Nephelometric Turbidity Units or NTUs. A maximum value of 5 NTU has been recommended by WHO for drinking water.

Electrical Conductivity: Electrical conductivity (EC) estimates the amount of total dissolved salts (TDS), or the total amount of dissolved ions in the water. EC is controlled by:

1. Geology (rock types) - The rock composition determines the chemistry of the watershed soil and ultimately the lake. For example, limestone leads to higher EC because of the dissolution of carbonate minerals in the basin.

2. The size of the watershed (lake basin) relative to the area of the lake - A bigger watershed to lake surface area means relatively more water draining into the lake because of a bigger catchment area, and more contact with soil before reaching the lake.

3. Other sources of ions to lakes - There are a number of sources of pollutants, which may be signaled by increased EC like Wastewater from sewage treatment plants, Wastewater from septic systems and drain field on-site wastewater treatment and disposal systems etc.

EC is measured with EC meters and represented by Ð'µS/cm (microsiemens/cm). EC meter consists of two metal electrodes that are exactly 1.0 cm apart and protrude into the water. A constant voltage (V) is applied across the electrodes. An electrical current (I) flows through the water due to this voltage and is proportional to the concentration of dissolved ions in the water - the more ions, the more conductive the water resulting in a higher electrical current which is measured electronically. Maximum value of 1000 Ð'µS/cm has been recommended by WHO for drinking water.

Total Hardness: Water is a good solvent and picks up impurities easily. Pure water -- tasteless, colorless, and odorless -- is often called the universal solvent. When water is combined with carbon dioxide to form very weak carbonic acid, an even better solvent results. As water moves through soil and rock, it dissolves very small amounts of minerals and holds them in solution. Calcium and magnesium dissolved in water are the two most common minerals that make water "hard." The degree of hardness becomes greater as the calcium and magnesium content increases and is related to the concentration of multivalent cations dissolved in the water. Originally, water hardness was understood to be a measure of the capacity of water to precipitate soap. Soap is precipitated chiefly by the calcium and magnesium ions present. Total Hardness is assessed by Titration methods and expressed as mg/l or ppm. Minimum value of total hardness is recommended as 250 mg/l and maximum value is 500 mg/l.

Calcium and Magnesium (Ca and Mg): Ca is one of the essential minerals required by the body for strength of skeleton, metabolism, and muscle activity and functioning of nerves. Therefore body needs it in amounts approximately 800 mg/day (20% from water) for adults. Mg has widespread metabolic functions thus is present in all body cells. Recommendable intake for men is 350 mg and for women is 300 mg. Toxicity is real in case of large consumption. The presence of Calcium in water supplies results from passage over deposits of limestone, dolomite, gypsum, and gypsiferous shale. Small concentrations of Calcium Carbonate combat corrosion of metal pipes by laying down a protective coating. Calcium and Magnesium are calculated with the titration method and expressed in mg/l.

Nitrates