Hardly. By any serious calculation, illegals consume less than 1% of the water in California. 80% goes to agriculture, and of the 20% that's left, the majority goes to landscape watering. Actual human consumption--toilets, drinking, showers--is about 8%, with affluent areas using more than poorer, and illegals make up about 10% of the population.
The fact is that California exports more water to China, locked as moisture content in alfalfa, than illegals consume.
Nice little trick the left plays with that 80% statistic: they only look at human consumption. The conveniently leave off the amount of water that is diverted for environmental uses like increased river flows for the Delta Smelt. I don't have the number nor the time to find it right now, but I believe the amount that is used for environmental "use" dwarfs what the humans - including the farmers that grow the food we eat - are using.
There is probably more water used just to keep golf courses in Palm Springs green than is consumed by every human in the state.
This also goes for Almond and Orange growers. I read that almond groves consume more water than every other crop.
The coastal cities of California, like San Diego, need to build desalinization plants. I was in Aruba recently. They have the second biggest desalinization plant in the world. After Israel. Aruba is a desert island. They get virtually no rain. Yet, I could drink the water right out of the tap and not worry about bacteria. They have plenty of water to irrigate, drink and swim in.
I still like my solution.