Is there an environmental quandary that's been keeping you up at night? Send it to firstname.lastname@example.org, and check this space every Tuesday.
Correction, Oct. 19, 2010: This sentence originally implied that when water sourced from a river flows down household drains, it is reused in the same water supply system. The water does stay in the same watershed, but is usually reused downstream by other cities and farms. (Return to the corrected sentence.)