In general it seems to refer to the fact that drinking and irrigation water is becoming more scarce in parts of the world and we need both technological and social systems for managing this resource. Aside from pure diminishing of water stock a practical example could be one country building a dam upriver from some other country.
I disagree: HN discussions are discussions, not blogs. The primary motivation for posting something here is to engage in a conversation. It's a very different form of writing as compared to blogging, for example. Running a blog is like running a 2nd business (in addition to your primary startup) - i.e. you have to spend a lot of time not just writing, but getting traction, promoting it, etc. Of course that would be a distraction for S&L, since building a search engine (not getting blog traction) was their goal.
