If earth is a watery planet then why we heard this slogan' save the water"?

Answer 1

Because there is lots of salty sea water but not so much clean fresh water. As the population grows there are more gallons of clean fresh water needed, but the supply is not growing.

Answer 2

Have you ever tried drinking sea water? How about irrigating crops with salt water? The lakes of the world contain so much industrial runoff, even today, they are not drinkable. Populations have grown up where there is little drinkable water. Water is not considered a cash crop so you will not get many people working to bring it to Phoenix or Albuquerque, or San Angelo.

Answer 3

because 90% of it is salt water, which you can't drink.
http://www.straightdope.com/mailbag/msaltwater.html

Only roughly 10% of the earths water is drinkable "Fresh" (ie no salt) water located in melting glacial springs, lakes and undeground wells. In certain desert areas, they have to collect rainwater in barrels and wait for the next rainfall to refill.
It is this small percentage of drinkable water that we want to save and keep clean.

We could evaporate sea water to remove the salt and water, but that is an expensive time consuming process, and as consumers we would end up paying alot to drink that water.

Answer 4

By and large water cannot be destroyed. We have about the same amount we had a billion years ago.