We must turn off the faucet and save water.
For the above construction, which of the below is more appropriate?
Debemos cerrar el grifo y ahorrar el agua.
Debemos cerrar el grifo y ahorramos el agua.
I would translate the original sentence,
We must turn off the faucet and save water.
as "Debemos cerrar el grifo y ahorrar agua", but more likely, as @fedorqui comments, I would write "Debemos cerrar el grifo para ahorrar agua", as "ahorrar agua" is the reason we must "cerrar el grifo".
Debemos cerrar el grifo para ahorrar agua.
orDebemos cerrar el grifo y así ahorrar agua.
We must turn off the faucet and save ourselves some water