The Marin Municipal Water District is proposing mandatory conservation rules for the first time since 1988 in response to record-low rainfall levels akin to those of the notorious 1976-77 drought. The proposed ordinance would require customers to limit outdoor watering to one day per week starting May 1 and adhere to other restrictions. The district board of directors plans to vote on the ordinance on April 20. The district has received just 20 inches of rain this year, its second-lowest amount in 143 years of records. The lowest was 18 inches in 1924.