If you're producing algae in bio-reactors, water-recycling of close to 100% can be reached, minus the water needed for the growth of the algae itself. Simply seperate the algae from the water, for example by centrifuging.
If you're doing the raceway thing, you could calculate/estimate the amount of evaporation given certain surface-areas, humidity-levels and temperatures.
With open soil crops, an unbelievably high percentage of water is lost through evapotranspiration and infiltration however, so I'd be surprised if that turned out to be a winner on this front. Closed-loop greenhouse horticulture might be a contestant though, but for energy-crops that's very unlikely to be economical at the current moment.
No problem! I need to to add though: since soil-based energy crops can be grown extensively instead of intensively, they could still work out in your favor if you have a certain amount of rainfall. By the way, found this article that quantifies water loss for open ponds: http://www.sciencedirect.com/science/article/pii/S2211926413001008
They put water loss without the evaporation of an open pond still at 0.03% of total volume per *day*.