Water is an essential element. Everybody on the planet needs water. To privatize water would be to discriminate some people from accessing water. Maybe they could not afford water. Water needs to remain public so that everyone has access to it as a resource. Everybody needs and uses water and it would not be fair to privatize it.
Water should be available to all people, not just private sectors and factions based on the fact that it surrounds us and is given to freely everyday from rain and streams. I understand that there is a cleaning process that is involved in it, but that does not give anyone the right to make it private, since it is a natural resource required by all walks of life to survive.