What you should never do when driving through deep or flowing water?

Avoid driving through deep puddles or flowing water if possible. If not, you should:
• Slow down and place transmission in a low gear.
• Gently put on the brakes. This presses linings against brake drums or discs and keeps mud, silt, sand, and water from getting in.
• Increase engine rpm and cross the water while keeping light pressure on the brakes.
• Maintain light pressure on the brakes for a short distance to heat them up and dry them out when out of the water.
• Make a test stop when safe to do so. Check behind to make sure no one is following, and then apply the brakes to be sure they work well. If not, dry them out further as described above. [California Commercial Driver Handbook]