Water is essential for life. Without fresh water humans cannot survive. Though a very large portion of the Earth is covered with water, one should not forget that most of it is water in the seas and the oceans which is salty and cannot be used to sustain human life.
The water that we need for our requirements has to be in the form of unsalted or fresh water, and there is a very limited amount of that on the Earth.
With an increase in human population and also an increase in per capita consumption of water, the amount of water that humans require is very close to approaching an unsustainable level. This would mean a situation where there is not enough water for everyone to survive.
This makes it essential for everyone to conserve water using all the methods that can be adopted. A majority of the ways to conserve water can easily be adopted by people and they would not require drastic lifestyle changes or a lot of effort.