In a slow sand filter, the element responsible for yielding bacteria free water is the: (A) Risk of Guinea worm infection, (B) Water is more than depth of 15 meter, (C) Where no water source in a distance of 1.6 km from community, (D) There is excess of Na+, K+, F+ salts
Answer is A. Level of hardness is expressed in terms of milliequivalents per litre where one milliequivalent is equal to 50mg calcium carbonate in one litre of water.
The level of hardness of hard water is equal to 3-6mEq/L or 150-300 mg/L.