San Marcos will start mandatory restrictions on outdoor water use on Monday. Residents will be allowed to water their lawns with sprinklers once a week, on a designated day.

"The primary impact of that is restricting their irrigation of their lawns and lawn watering," said Tom Taggart, director of water and wastewater for the City of San Marcos.

The city will allow designated watering days based on the last number of addresses. Residents whose addresses end with zero or 1 may water on Mondays; 2 or 3 may water on Tuesdays; 4 or 5 may water on Wednesdays; 6 or 7 may water on Thursdays; and 8 or 9 may water on Friday.

Irrigation with hand-held buckets, hoses or soaker hoses will continue to be allowed at any time, and at-home car washing will be allowed one day a week, on a designated day.

At the same time, the city will require owners of swimming pools to keep the pools at least 25 percent covered when not in use to reduce evaporation.

The city is asking restaurants not to serve water to customers unless it is specifically requested.

"We would ask all citizens not to use water unless they absolutely need to for things are washing cards or any discretionary uses of water," Taggart said.

Austin has implemented a similar, but slightly more lenient, restriction on watering lawns. Austin allows residents to water twice a day, again on designated days, until the end of September.

On Monday, San Marcos will enter Stage One restrictions, which mean the Edwards Aquifer is expected to be drop under 650 feet over the next 10 days. If the aquifer drops to less than 640 feet, the city will move to Stage Two restrictions, which further limit the times lawns can be watered and cars can be washed.