Question

why we save water as earth is filled 70% of it

Answer 1

we save the water to live . You are saying that water is 70 % on earth but the distribution of water is non uniform In every part of earth so we should conserve it .

Answer 2

hii
as we know earth is filled with 70% of water but after that we need to save the water because in very less amount fresh water is present and after subtracting the fresh water from 70% of water we'll found that their is large amount of saline water which is unable to use. atlast we should always try to save the water.
i think its help you