California employers are required to take these four steps to prevent heat illness:

1. Training
   Train all employees and supervisors about heat illness prevention.
2. Water
   Provide enough fresh water so that each employee can drink at least 1 quart per hour, and encourage them to do so.
3. Shade
   Provide access to shade and encourage employees to take a cool-down rest in the shade for at least 5 minutes. They should not wait until they feel sick to cool down.
4. Planning
   Develop and implement written procedures for complying with the Cal/OSHA Heat Illness Prevention Standard.

http://www.dir.ca.gov/dosh/heatillnessinfo.html