Point-of-Use (POU) water treatment refers to a variety of different water treatment methods (physical, chemical and biological) used to improve water quality for an intended use (drinking, bathing, washing, irrigation, etc), at the point of consumption instead of at a centralized scale (involving a distribution network). POU treatment encompasses water treatment at a more decentralized scale like in a small community or at the household level; furthermore, safely storing water (especially unclean water) is a huge challenge, therefore upon water use, a POU treatment method (below) can be applied to improve the water quality 

http://en.wikipedia.org/wiki/Point_of_use_water_treatment