In a slow sand filter, the element responsible for yielding bacteria free water is the
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.
Risk of Guinea worm infection
Water is more than depth of 15 meter
Where no water source in a distance of 1.6 km from community
There is excess of Na+, K+, F+ salts