Sorry, but no cigar. Agriculture uses 80% of the water in California. Of the 20% that's left, most goes to landscaping--a lot of it to the 125 desert golf courses in the Palm Springs area. About 8% goes to actual household use, with affluent areas using more per person than lower income areas. Illegal aliens make up approximately 10% of the population, so it's hard to make a case they use more than 1% of the water.
Illegals are also the cause of Climate Change and the decline in the honeybee population. I wouldn’t be surprised if there was a link between the increase in illegals and the problems with Bruce Jenner.