Should we reduce the usage of water!

Why there is water usage shortage issue in Malaysia? I guess the main reason is due to dry season.
To me, the usage of water per capital over 300 liter is not really the issue here. The statement said if residents in some states in Malaysia, not reduce usage of water, then in 2014, there will be crisis of shortage water. How far it is true?
As we all know, after we use the water, the waste water will flow to drain and start it cycle of evaporation, form cloud, and condensation of atmospheric water vapor into drops of water heavy enough to fall, as rain.
We should use water wisely because the process of purifying the water is costly!