This is a collection of links with data and information about the California reservoirs, snowpack. and other water related topics.
The CDEC site is the chief source of information on California reservoirs and snowpack status.
The US Drought Monitor has the most comprehensive info on drought conditions in the US as well as California..
The USGS has a very nice page with lots of beautiful data visualisations of the drought.
The CDEC also has official California Snowpack data.