Water footprint benchmarking

We are working in my research group on developing benchmarks for water footprints of crops. Let me know if you have any specific idea on how to establish 'reasonable' benchmarks. If say 25% of the farmers can produce wheat with a water footprint of 1200 m3/ton or less, why not set that as a benchmark for the other 75%? But why choose 25% and not 10%. That may be a matter of feasibility and costs... but also a a matter of ambition and need. Any ideas are welcome.