These are mainly due to various chemical substances from industry which get into public water supply. Usually they contain solvents, detergents, heavy metals, dyes, pigments, sulphides, organic substances etc.
The accidents in various types of industries like manufacturing, power production etc. and in storage and transportation of various hazardous materials used in these industries fall under this category.
There are various ways of causing fire hazards. These are: (a) The butts of cigarette are "discarded carelessly. (b) Throwing of loose waste papers on the floor. (c) Matches are placed in the stands with the head exposed.