[blank] no desperdicie el agua. - "[blank] I did not waste the water."
Estoy triste de que = I am sad that
Tengo miedo de que = I am scared that
Es une lástima que = It is a shame that
Es importante que = It is important that
It can't be a negative thing that you didn't waste the water, so the first 3 options don't make much sense.
Answer:
Es importante que no desperdicie el agua.
Espero ue esto te ayude.