Soaking in warm water is one of the oldest forms of medicine, and there’s good reason why this practice has stood the test of time. Research has shown warm water therapy works wonders for all kinds of musculoskeletal complaints, including fibromyalgia, arthritis and low back pain.

“The research shows our ancestors got it right. It makes you feel better. It makes the joints looser. It reduces pain and it seems to have a somewhat prolonged effect that goes beyond the period of immersion,” says Bruce E. Becker, MD, director of the National Aquatics & Sports Medicine Institute at Washington State University in Spokane.

There are many reasons soaking in warm water works. It reduces the force of gravity that’s compressing the joint, offers 360-degree support for sore limbs, can decrease swelling and inflammation and increase circulation. 

So, how long should you soak? Dr. Becker says patients he’s studied seem to reach a maximum benefit after about 20 minutes. And make sure you drink water before and afterward to stay well hydrated.

Here are some other simple steps to make the most of your next bath.

Go warm, not hot. Water temperatures between 92 and 100 degrees are a healthy range. If you have cardiovascular problems, beware of water that’s too hot because that can put stress on the heart. The U.S. Consumer Product Safety Commission says anything over 104 degrees is considered dangerous for everyone.

Don’t just sit there. Warm water is great for relaxing, but it is also good for moving. Warm water stimulates blood flow to stiff muscles and frozen joints, making a warm tub or pool an ideal place to do some gentle stretching. To ease low back pain, trap a tennis ball between the small of your back and the bottom or back of the tub, then lean into it and roll it against knotted muscles. The flexibility lasts even after you get out, says Ann Vincent, MD, medical director of the Mayo Clinic’s Fibromyalgia Clinic in Rochester, Minn. “Patients report that soaking in a warm bath and stretching after that seems to help.”

Add some salts. Data collected by the National Academy of Sciences show most Americans don’t get enough magnesium, a mineral that’s important for bone and heart health. One way to help remedy that: bathing in magnesium sulfate crystals, also known as Epsom salts. They’re relatively inexpensive, can be found at grocery and drug stores and can boost magnesium levels as much as 35 percent, according to researchers at the University of Birmingham in the United Kingdom. But don’t go overboard; the National Institutes of Health warns these salts should only be for occasional use. People with diabetes should be aware, too, that high levels of magnesium can stimulate insulin release.

Consider finding a warm water pool. Warm water can be so helpful in fighting the pain and stiffness of arthritis and fibromyalgia that experts recommend heated pools for exercise. A variety of studies of patients with both conditions found that when they took part in warm water exercise programs two or three times a week, their pain decreased as much as 40 percent and their physical function increased. The exercise programs also gave an emotional boost, helped people sleep better and were particularly effective for obese individuals.

“We definitely talk to our patients about that,” Dr. Vincent says. “You are in a pool so you aren’t working against gravity, warmth is comforting and the heat can decrease stiffness and possibly improve circulation.”

The Arthritis Foundation offers an Aquatic Program in which participants are led through a variety of exercises in warm water.