Michael Mascarenhas asks "how do we actually measure this complex activity known as water access in subsistence communities?" and, as his article shows, it is a genuine problem. In rural Africa it's difficult to imagine any centralised system of programme funding allocation and assessment working well. The well-being of an individual or community, while it is likely to be accurately perceived by insiders, would be difficult to quantify in a way that's useful to national or NGO decision makers.
But the Social Policy Bond approach could help. Rather than try to measure such abstract concepts as 'availability', it would instead focus on, and target, the benefits that such availability will have on verifiable outcomes: infant mortality, morbidity, longevity, birth weights, to give a few possibilities. It would be a shame, I think, if the failed paradigms of the west - the implicit or explicit targeting of such close-to-meaningless accountancy-type abstractions as 'the economy', GDP etc - were to be adopted by the developing countries. They have led us astray, quite dramatically; with the full ramifications yet to be felt.