Bathing horses may not seem like a hazardous activity, but the wash stall is a common site for accidents. To keep both you and your horse safe:
Be on watch for slick floors. While bathing horses, water and soap make for slippery surfaces in a wash stall. Consider using mats that allow drainage or have grooves carved into the concrete floor of the wash stall to provide more traction.
Mind the hose. A hose threaded between hind legs can startle or entangle a horse, while bathing horses. You can also trip yourself up if you're not careful. Use a hose that's long enough to give your horse a wide berth as you work and keep track of it's position at all times.
Don't start a fight. Remember that most horses simply tolerate bathing so work quickly and try to make the experience as pleasant as possible. For example, when washing your horse's face, use a wrung out sponge or damp rag instead of a sprayer.
Remove unnecessary objects from the area. Extra buckets and equipment can only cause trouble if left in the wash stall while you are bathing your horse.