Q13Basic Civil Engineering

Ensuring the safety and quality of raw water for municipal or industrial use requires the rigorous evaluation of several chemical characteristics. These chemical parameters indicate the presence of dissolved minerals, gases, and potential pollutants. Four of the most critical chemical characteristics of raw water include pH, Total Hardness, Chlorides, and Dissolved Oxygen (DO).

1. pH (Potential of Hydrogen): The pH value is an indicator of the acidity or alkalinity of the water sample, representing the negative logarithm of the hydrogen ion concentration. Highly acidic water causes severe corrosion in plumbing systems, while highly alkaline water leads to scaling and reduces the efficiency of chlorination. - Method of Analysis: pH is typically measured using an electrometric method with a calibrated digital pH meter equipped with a glass electrode. It can also be estimated using colorimetric methods with universal indicators. - Acceptance Value (IS 10500:2012): The acceptable limit for drinking water is strictly between 6.5 and 8.5.

2. Total Hardness: Hardness in water is primarily caused by the presence of dissolved multivalent metallic cations, predominantly calcium ($C{a}^{2+}$) and magnesium ($M{g}^{2+}$). Hard water prevents the lathering of soap, increasing soap consumption, and causes severe scale formation in boilers and industrial pipes. - Method of Analysis: Hardness is analyzed using the EDTA (Ethylenediaminetetraacetic acid) complexometric titration method. Eriochrome Black T (EBT) is used as the indicator, changing color from wine-red to blue at the endpoint. - Acceptance Value (IS 10500:2012): The desirable acceptable limit is 200 mg/L (as $CaC{O}_3$). In the absence of an alternate source, the permissible limit is extended to 600 mg/L.

3. Chlorides: Indicate pollution by sewage or industrial waste. 4. Dissolved Oxygen: Essential for aquatic life and indicates the level of organic pollution in a water body.