Although the state has mandated a 25% reduction, so far they are leaving it up to the hundreds of local water districts, how to achieve that level of reduction. Each local district has published their preliminary restrictions, most include some level of restriction on lawn & garden watering. Some just say no lawn watering during daytime hours, some say its only allowed 1 or 2 days a week, some say its only allowed on days they say its ok. Once a district determines that these preliminary restrictions are not meeting the 25% requirement and they face $10,000 a day fines, they may prohibit all lawn watering completely.
In addition to these specific restrictions by district, the water rates are going to be significantly increased based on usage levels, the more you use the higher per gal cost, so that even if its allowed, you may not be able to afford to water a large lawn unless you have an unlimited budget. At $500 per gallon that green lawn and flower bed may not look as nice.