The Holy Prophet (S.A.W.) attached great importance to water, and prohibited the excessive use of it even when taking the ablutions, "When he saw that Saa'd was using a lot of water, he said: "What is this? You are wasting water." Saa'd replied asking: "Can there be wastefulness while taking the ablution?” To which he replied: "yes, even if you take them on the bank of a rushing river." So we should use water economically.
As Muslims, we are prohibited from polluting water. He said, "None of you should pass his urine or bathe in a water source." (Bukhari)