Personally, most of my minimal landscaping is either native or from other Mediterranean climate zones, so you might take a look at the water needs of what you have in place now. Two other things I have seen mentioned are the timing of your watering (early am or evening vs. daytime when there is more evaporation) and an increase in duration/decrease in frequency in your watering.

Your local water company may have some suggestions on its website, too, so take a look.

Just to start with:
Put in drought tolerant or native plants and remove all grass. Natives don't like drip irrigation, just water for the first year. A lot of drought tolerant and native plants are also recommened by fire depts. LA county recommends all salvias/sages and french lavender. I would think OC would also, you might check their website if in a brush area.
Adjust sprinklers so no or little runoff.
Mulch, mulch, mulch.
A Western Garden Book has tons of info.

Here's a great site to look at also:
http://www.laspilitas.com/garden/Drought_resistant_plants_for_a_California_garden.html

Here is a link that might be useful: be water wise

Zones: group thirsty plants together, xeriscape plants together so that irrigation can be minimized, yet all the plants will get what they need.

If you really need a lawn (kids, pets), you really need a lawn. "Verde" hybrid buffalo grass or Carex pansa instead of much thirstier fescue.

But if you don't need a lawn, look at alternatives like Dymondia (silver carpet) groundcover around flagstones. Dymondia does very well being watered once every two weeks or so in summer and not at all in winter.

A lawnless front yard is becoming more acceptable due to the drought.

Don't wash off your driveway and sidewalks with the hose (does anyone do that any more?).

What everybody else said, plus:

1) Mulch helps reduce evaporation and allows you to water less frequently.

2) Save water elsewhere so you won't feel so guilty watering a few thirsty shrubs: install low-flow showerheads and low-flow toilets, and put aerators on your kitchen and bathroom faucets.

3) Install a couple of rain barrels. By capturing rainwater from your roof in the winter, you'll be able to supplement winter rainfall and water your plants a month or so into the dry season without turning on the tap.

4) Use greywater on houseplants and containers: when you run the water to get it hot, or boil water for pasta or vegetables, save it. If you have leftover coffee or tea in the morning, your plants will thank you for it.

Put a bucket in your bathtub to catch the water from the shower while it's warming up. Use that to flush the toilet! You'll get a bucket per shower, which does two flushes: that really adds up.

That way I don't feel as bad about watering my community garden once a week, by hand.

We have drip hoses everywhere in the yard, for flowers, fruit trees and vegetables. We have a well and it cost a lot to power the pump. I like knowing that the water is only going where I want it to and not growing weeds. I try to pick the emitter that provides just the right amount of water for the plant it is watering. Each plant/tree/shrub has it's own needs met. We also use a lot of mulch. I only turn on the water 2-3 times a week, depending on the weather.

Also--eat one less pound of beef this year. I just read that it takes as much water to produce one pound of beef as you use to shower for an entire year.

You could water a lot of plants with that.

Lots of great advice. I'll just add that I love soaker hoses. I have them in my potager and several other beds. I also have sprinkler heads that don't spray way up in the air and waste water. They're almost like bubblers but go out further.

Also, most new appliances use far less water than older ones. My KA dishdrawers use just a few gallons of water and do a great job of getting the dishes clean, and I have really crummy water pressure. And the front loader washing machines can use 1/3 to 1/2 the water as a regular machine. I emptied my frontloader waste water into a 33 gal. trash can and it filled it about half full. It would have been overflowing from my old machine.