This number is supposed to belong to the Orange County Water District. I've received three calls from them today which i did not answer and no message was left. Apparently someone has hacked their number.
They didn't "hack" the number, but are probably spoofing it to appear legitimate. If you're near the area, callers may have done enough homework to spoof local numbers for a better chance to get an answer. It's doubtful OCWD is behind the calls.