Water is energy. Not literally, of course (the square of the speed of light notwithstanding), but practically. Naturally moving water can be made to yield energy, either directly or through hydroelectric generation. Unnaturally moving water (like what comes out of the faucet) consumes a tremendous amount of energy, necessary to make it follow a path of greater resistance.
The STARS  rating system for campuses recognizes the energy consumption of water by giving points for use of non-potable water for irrigation purposes. Graywater (slightly used, lightly soiled) generally works fine on most vegetation, and giving that water a second use decreases the energy necessary for overall water processing and delivery. Captured rainwater (while technically potable if handled properly) has many of the same virtues.
So I was unsurprised to see a recent post to the Green Schools list (GRNSCH-L@listserv.brown.edu). A sustainability administrator in upstate New York asked whether other schools had experience in capturing rainwater and using it to irrigate athletic fields. Perfectly logical question.
What surprised me was a response posted by another administrator at a school in Colorado. It made reference to water law in the western USA making rainwater capture generally illegal.
The overall concept of water law and water rights seems entirely valid -- if you live downstream and depend on a river, you don't want the folks who live upstream either fouling that river or damming it and cutting off your flow. But the idea that a raindrop would be subject to the same legal treatment had never occurred to me. Cisterns, whether fed by springs or by downspouts from the roof, have been used on farms for centuries. They stored (and sometimes, still store) drinking water both for people and for livestock. The idea of setting up a cistern system (by whatever newfangled name) for irrigation purposes seems entirely non-controversial.
Think about it -- a campus takes the rainwater which falls on building roofs, stores it for a bit, then runs it out onto (or into) the ground. If the cistern weren't there, the rainwater would flow off the roof onto the ground (similar ground, not very far away) anyway. If the whole building weren't there, the rainwater would have fallen directly onto the ground (similar ground, not very far away) in the first place. Where there's no measurable effect, there's no harm. Where there's no harm, there's no foul (remember, it's athletic fields we're talking about, here). What's the problem?
Apparently, the problem lies in long-established legal doctrine which prioritizes water use based on who started using it first. If my farm, downstream, started pulling water from the river in 1910, your new farm (upstream) can't draw water levels down below what I need. However, if my older farm is upstream, I have no particular obligation to leave enough water in the river for your newly established demands. I'm absolutely certain that the actual law is both far more complex and far more subtle than that, but I think I've got the general principle more or less right. (Request to legal scholars -- help me out here. Any useful discussion or case references would be more than appreciated. Please email me  and point me in the right direction. I'll share whatever I learn.)
From a sustainability perspective, this sort of legal doctrine (if I'm even close to understanding it correctly) is potentially troubling. The fact that somebody's been using a resource for a long time doesn't mean they're using it efficiently or effectively -- in fact, the correlations may well be negative. "First use" isn't "best use". And for scarce resources, "best use" (however easy or difficult to define) is what we need.
I'm sure that other laws, governing other resources, in other states, present similar challenges. Anybody want to share any examples?