The study found that saline solution reduces painful inflammation of the joints without any unpleasant side effects.
Scientists say the breakthrough could revolutionise how the condition, which afflicts millions, is treated, the 'Daily Express' reported.
Even ordinary table salt in high concentrations can be used and, unlike conventional drugs, there are no unpleasant side-effects.
The Manchester University team investigated how the way in which the body's cells expand can control inflammation, which is the immune system's first response to injury or infection.
In the tests on mice, they discovered that by injecting a saline solution into an area of inflammation the swelling was reduced by sucking the water out of the expanded cells.
"This research opens up exciting opportunities. What we've identified has the potential to be used to help so many patients," Vincent Compan, of Manchester University's Faculty of Life Sciences, said.
Compan and Dr Pablo Pelegrin found cells in the bodies of arthritis sufferers expand but salt water can reduce the swelling by dehydrating them.
The salt worked the same whether it was injected into the body or absorbed through the skin via bandages soaked in saline or bathing.
This explains why hot springs which are high in salts are so effective and for years were frequented by patients seeking a miracle cure.
"We have found that hypotonic solutions (low in salt) strongly activate inflammation at molecular level," Pelegrin said.
"Conversely, the use of hypertonic solutions (high in salt) was a potent inhibitor of such inflammatory signals at molecular level.
"Therefore, osmotherapy (dehydration) with hypertonic solutions could be beneficial in the management of inflammatory joint diseases, such as rheumatoid arthritis, either by prolonged soaking or by vapour pressure techniques," said Pelegrin.
At present there is no cure for arthritis but a number of treatments in place that can help slow down the progress of the condition.
