Why are we always said to conserve water even though it's a renewable resource?
Population is increasing and per capita consumption is also increasing. It is precious (especially when it is not found in great amount)
Some impurities in water stay in it forever.
Water is not and endless resource (such as solar energy). Especially fresh water. Salty water is difficult to treat (costly).
When you find water in great quantity, you do not want to pay for it (because it is plenty). However, when you find only a drop (if especially you are thirsty for a while), it is priceless.
That is why conservation of water is a crucial issue. Especially for freshwater resources.