Water at Dawn or Dusk
The middle of the day is the least efficient time to water your plants. According the the U.S. Environmental Protection Agency's (EPA) WaterSense Program, up to 30% of water can be lost to evaporation during midday. At dawn and dusk, when the sun is low in the sky, evaporation rates are minimal and the wind tends to be calm enough that it doesn't blow water away.
If you have an irrigation controller, program it to water at dawn or dusk. If you water by hand, plan to do it immediately after something you already regularly do in the early morning or evening (e.g. after eating breakfast).