STATE WATER OFFICIALS HAVE REPORTED OVER 200,000 CALIFORNIA HOMES DO NOT HAVE WATER METERS.    A RECENT STUDY BY THE ASSOCIATED PRESS REVEALED THAT RESIDENTS WHO LIVE IN WATER DISTRICTS WITH THE MOST UNMETERED HOMES USE MORE WATER EACH DAY THAN THE STATE AVERAGE. ADDITIONALLY MANY STATE WATER AGENCIES ARE UNCERTAIN IF THEY ARE CONSERVING 20%, THE GOAL SET BY GOVERNOR JERRY BROWN EARLIER THIS YEAR.     HOMES BUILT AFTER 1992 WERE REQUIRED TO HAVE METERS, BUT ALL OTHER HOMES HAVE UNTIL 2025 TO BE RETROFITTED.    AROUND 40 WATER DISTRICTS CONTINUE TO CHARGE CUSTOMERS A FLAT RATE FOR WATER USE.