What does this equation mean?

Water Usage Effectiveness, the metric LBNL uses throughout its modeling, is defined analogously to the more familiar Power Usage Effectiveness: $\mathrm{WUE_{site}} = \frac{V_{\mathrm{water}}}{E_{\mathrm{IT}}}$. where $V_{\mathrm{water}}$ is total on-site water consumption in litres and $E_{\mathrm{IT}}$ is the electricity delivered to IT equipment, giving WUE units of litres per kilowatt-hour rather than PUE’s dimensionless ratio [ 4 ] . What LBNL’s simulations across roughly 965 US weather stations and multiple facility archetypes show is that this number is driven overwhelmingly by which heat-rejection route a facility uses at the plant level — an economizer decision layered on top of, and largely independent from, the cooling method at the rack. Facilities running “water-cooled chiller systems without economizers exhibit the highest WUE, largely attributed to substantial cooling tower water usage,” and this pattern holds for both air-cooled and liquid-cooled IT equipment alike when both sit behind a waterside economizer [ 4 ] . Conversely, facilities using airside economizers “allow for the shutdown of chilled water systems during favorable weather conditions, resulting in substantial water conservation,” regardless of whether the racks behind them are air- or liquid-cooled [ 4 ] .