Official California state government water supply stats. I'm not entirely sure there's an API here but there is interactive graphing that can probably be reverse engineered to get data. The hydrologic overview and reservoir conditions are of particular interest.
This project is a software defined radio receiver for these messages. We make use of an inexpensive rtl-sdr dongle to allow users to non-invasively record and analyze the commodity consumption of their household. Designed with ERT-compatible smart meters i mind.