Equine Bathing

A sweat scraper should be used to remove the excess water from the horse's body every time you bathe or hose a horse. Removing excess water is necessary because water acts as an insulator, trapping the heat against the body and preventing a hot horse from cooling down. A sweat scraper is simply a "squeegee" for horses, and it is used in a similar
manner. To sweat scrape your horse, begin at the top of the neck - while applying a little pressure, pull the scraper down the neck following the direction of the hair. Continue to repeat this process working your way down the horses back and finishing with the belly.
After the bathing is complete and you have removed the excess water with a sweat scraper, let your horse dry while securely cross-tied or by hand walking in the sun. Hand walking on a hard surface or in grass will lessen the amount of dust that will settle on the horse and will help speed drying. Remember to never turn a horse out to pasture while still wet as they will immediately roll and undo all of your hard work! If you must wash when it is cold outside, keep your horse inside away from drafts and use a cooler or an anti-sweat sheet for drying. Think of a cooler as a bath robe for horses - it will help wick water out of the coat and allow your horse to dry quicker and stay warm.

Source http://www.ecmagazine.net/manage_pdfs/bath.pdf