All industri which has an activity which contains water in their production normally have a need to purifytheir wastewater. What kind of wastewater soulution the requires depends on how polluted the water is and where the water is supposed to be dropped back. 

Another type of water which may be purified is surface water which directly or indirectly pollutes in contexts with rainwater. This process will lead to contamination of the nature, and therefore this water may need to be purified.