Because there was no need. Reservoirs were full and residents conserved: http://www.santabarbaraca.gov/gov/depts/pw/resources/system/...

FWIW, this explains why it will take 20 mil to get it back on line: http://www.noozhawk.com/article/santa_barbara_desalination_p... One eye-opener: reverse osmosis membranes break down with disuse so they were sold to Saudi Arabia.