<prompt> Hardness of water is expressed as milli-equivalent per litre mEqL, one unit of which is equivalent to which one of the following -20 mg CaCO3 20 ppm30 mg CaCO3 30 ppm40 mg CaCO3 40 ppm50 mg CaCO3 50 ppm  <response>: Hardness of water us expressed in milliequivalentsL. One mEqL is equal to 50mg of CaCO350 ppm in one litre. Parks Textbook of Preventive and Social Medicine, 25th edition, Page No. 786 