“…Lime, soda ash and caustic soda may be used depending on the economics of the problem. Hopkins, Armstrong, and Baylis (8) have studied the question of the best treatment for the average American community and find that for waters with an initial hardness below 75 p.p.m., lime treatment is the correct one. When high acidities are noted as due to free CO2, a previous aeration may reduce the cost of lime treatment.…”