in chapter" water" says that water is a limited resource and i agree with this but after a million or more than million years ago when fresh water is empty. what do we do?

Without water no life can exists. Water is rotating in the environment in a cycle which includes absorption, condensation and precipitation. If we can use the water resource coming by this method following the cycle in a sustainable manner (without wastage) water will never disappear. The water cycle continuously supplies water to us. But if we cannot stop misuses and excess consumption of water, then one day will surely come when there will be no fresh water available. Transformation of salt water into edible form is almost impossible and highly expensive. So this is the high time to conserve water for us and for our future generations.