1. Impurities come at the source.
Water composition depends upon geological factors. Quality of water is greatly affected by its place of origin and the path it follows, e.g., water will have biological contamination if it is flowing along a crematorium.
Water from the well of lime water is heavy because of the calcium present in it. Drainage of sewer into the main stream of water makes it unfit for human usage. Sometimes water becomes impure because of certain negligence like bathing, washing of clothes and utensils near the water source.
2. Impurities come during transit. Water becomes impure during transit in dirty utensils.
3. Impurities come during storage.
Despite utmost precautions in water storage, water loses its luster after sometime. In earthen pots, water is cooled and gets fresh air but when these pots get holes the water becomes impure due to the mixing of dust. Sometimes tiny organisms creep into the pots. Metal pots do not allow the flow of dust particles through them, but at the same time they prevent the circulation of air.
4. Impurities come during distribution. Water becomes impure by the chemical reaction of certain substances present in the metallic pipes through which it is distributed. Underground pipes for the distribution of water should be separated from the sewage and gas pipes, otherwise there is always a possibility of water contamination.