Over at On The Public Record, there's some freewheeling conceptual thoughts about the impending drought situation in California. In comments, Emily Green suggests that Assembly Bill 1881 be made retroactive. Not having a particularly good memory, I went and looked it up. AB 1881, signed into law in 2006, mostly has to do with outdoor water use efficiency and it mandated that by Dec 31, 2010, that all municipalities have an ordinance on their books that was at least as strict as a suggested model law. Most new and rehabilitated landscapes are now subject to this water efficient landscape ordinance. Public landscapes and private development projects including developer-installed single family and multi-family residential landscapes with at least 2500 sq. ft. of landscape area are subject as well. Homeowner provided landscaping at single family and multi-family homes are subject to the [State or local standards] if the landscape area is at least 5000 sq. ft. As it turns out, I blogged about it earlier, mostly with a hopeful thought that it would make a difference, as I recall.
There's already retroactive component for landscapes larger than 1 acre, which I suppose applies to public parks and the landed gentry, but the language says that they "may" be subject to a water audit, not that it is compulsory. Also, existing landscapes get additional latitude with regard to water used - about a 10% bump up from AB1881 standards for new construction with regards to the evapotranspiration rate and a [presumably very] relaxed set of water use criteria dating from 1992.
I have discovered a proof of how truly remarkable the water savings could be if it were made retroactive which the margins of this post are too small to contain.* Perhaps we need wait only three centuries for a complete explanation.