Who'd a thunk it? Kevin Costner goes from appearing in a disaster about water to perhaps being a real hero of the Gulf oil disaster:

Desperate times call for desperate measures. So with hundreds of thousands of gallons of oil still spewing into the Gulf of Mexico each day, and its corporate image starting to resemble the tar-covered sea creatures now washing on to Louisiana's fragile shoreline, BP has called on Kevin Costner to help stave off environmental Armageddon.

The Hollywood star has been bobbing around the Mississippi Delta helping representatives of the British oil firm and US coastguard test-drive a stainless steel device called the Ocean Therapy. In a claim which sounds as unlikely as the plot premise of Waterworld, he says it can quickly and efficiently clean oil from tainted sea water.

Bizarrely, Costner may be on to something. The actor has spent 15 years and roughly $26m (£18m) of his personal fortune developing the patented machine with the help of his elder brother Dan, a scientist. It works like a giant vacuum cleaner, sucking up dirty liquid and then using a high-speed centrifuge to separate it into oil, and heavier water.

When he allowed the local media to see Ocean Therapy in action – albeit on dry land – it appeared to work as advertised. Yesterday, six of the devices were attached to boats and floated into the Gulf, so the organisers of the clean-up operation could see whether they might also be capable of functioning on the high seas.

"This is a technology that we know works, and has worked for a long time," Costner said, adding that 26 of the machines are now in Louisiana ready to be put into action. "I'm just really happy that the light of day has come to this, and I'm very sad about why it is. But this is why it was developed, and like anything that we all face, as a group, we face it together."

Costner, 55, has quietly been developing Ocean Therapy since the mid-1990s when he founded the Costner Industries Nevada Corporation, a company which funded eco-friendly research by his brother and a team of scientists. Aside from the water cleaning device, the firm has also invented a non-chemical battery.

Each of the 26 Heath Robinson-style machines now in Louisiana waiting to be deployed can clean between 5 and 200 gallons of water a minute, depending on its size, said Costner's lawyer and business partner, John Houghtaling, which means they could in theory mop up oil at the rate it is currently gushing into the Gulf. Polluted sea water which passes through them comes out 97 per cent clean.

"Kevin saw the Exxon Valdez spill, and as a fisherman and an environmentalist, it just stuck in his craw, the fact that we didn't have separation technology," said Houghtaling. "Kevin wrote all the checks for this project. This was one man's vision. Sometimes it takes a star to come in with their money and time to make a difference."