Answer :

It depends on what the reaction is. Usually H2O is neutral. If in the reaction, it accepts proton(H+), it is base. If it donors the proton(H+), it is acid. So it based on what reaction it is.

Answer: both an acid and base

Explanation: By Bronsted-Lowery acid base theory: proton Donor is acid and proton Acceptor is base.

Here H2O by donating the proton acts as acid.

H2O ------> H^+ + OH^-

And by accepting the proton acts as base

H2O + H+ --------> H3O+