The accurate description of the thermodynamic and dynamical properties of liquid water from first-principles is a very important challenge to the theoretical
community. This represents not only a critical test of the predictive capabilities of first-principles methods, but it will also shed light into the microscopic properties of
such an important substance. Density Functional Theory, the main workhorse in the field of first-principles methods, has been so far unable to properly describe water
and its unusual properties in the liquid state. With the recent introduction of exact exchange and an improved description of dispersion interaction, the possibility
of an accurate description of the liquid is finally within reach. Unfortunately, there is still no way to systematically improve exchange-correlation functionals and
the number of available functionals is very large. In this article we use highly accurate quantum Monte Carlo calculations to benchmark a selection of exchange-correlation
functionals typically used in Density Functional Theory simulations of bulk water. This allows us to test the predictive capabilities of these functionals in water,
giving us a way not only to choose optimal functionals for first-principles simulations, but also giving us a route for the optimization of the functionals for the system at hand.
We compare and contrast the importance of different features of functionals, including the hybrid component, the vdW component, and their importance within different aspects of the PES.
In addition, we test a recently introduce scheme that combines Density Functional Theory with Coupled Cluster Calculations through a Many-Body expansion of the energy, in order to
correct the inaccuracies in the description of short range interactions in the liquid.