The grand canonical Monte Carlo technique was employed to simulate the behavior of water confined in open asymmetric slit-like nanopores, as formed by parallel hydrophilic and hydrophobic walls. Both structureless nonorienting and structured orienting walls were studied. At a chemical potential slightly above its liquid-vapor bulk coexistence value, an unusual phase state of water was observed, characterized by giant fluctuations of the number of water molecules and a wandering liquid-vapor interface.