British researchers found drinking silicon-rich mineral water "significantly reduced" the levels of neurotoxin aluminium in the body, potentially slowing decilne in Alzheimer's patients.
Aluminium has long been linked to the development of Alzheimer's but no scientific relationship has yet been proved.
One patient saw the amount of aluminium in their body drop by 70 per cent and three participants actually showed an improvement in their mental health.
Professor Christopher Exley, of Keele University, who led the research, said the "surprising" results gave hope to findings ways to combat the devastating disease.
He said: "There were two parts to our research. The first is that drinking silicon water does remove aluminium from the body.
"When you drink silicon-rich mineral water aluminium throughout the body is gathered up into the blood and then excreted through the urine.
"It seems to purge the aluminium from the body. We now know we can use this silicon-rich 'therapy' water to reduce aluminium.
"The second part of our research was looking at the cognitive abilities of people with Alzheimer's and whether these changed as the aluminium was reduced.
"The most interesting thing was that we did see this potential relationship between the removal of aluminium and the positive improvement in cognitive function.
"It is highly unlikely to see changes over such a short period of time so the fact we saw changes in cognitive ability was quite a surprise.
"We saw improvement in some cases, cognitive function remained the same in others and it did decrease in others."
Previous studies have linked the prescence of aluminium with plaques and tangles - two kinds of microscopic damage - in the brains of people with Alzheimer's disease.
Researchers examined the aluminium levels of 15 sufferers and their carers or partners - 15 women and 15 men in total.
The brand of water used in the study - published in the Journal of Alzheimer's Disease - was a Malaysian water called 'Spritzer', which has high levels of the chemical element silicon.
Brands on sale in Britain with similar levels include Volvic and Fiji water.
Scientists asked the participants to drink a litre of Spritzer water every day for 13 weeks and measured their aluminium levels at the end.
The patients saw a huge reduction in their aluminium levels, with a number showing drops of 50, 60 and 70 per cent.
Participants were also assessed using the ADAS-Cog (Alzheimer Disease Assessment Scale-Cognitive) method, which is a recognised 11-part test.
The tests include memory questions and 'simple' tasks such as drawing a clock face - people with a deteriorating function may struggle to put the numbers in the right place.
After 13 weeks, cognitive function is eight of the 15 Alzheimer's sufferers had not deteriorated - and actually improved "substantially" in three.
Professor Exley added: "We now want to carry out further research to see if we could reduce the risk of Alzheimer's who seem to be predisposed to it.
"They are usually aged between 40 and 60. If we could get people to include silicon-rich water in their diet in the future and reduce their risk, it would be a great."
The Spritzer mineral water containing 35mg of silicon per litre.
However, Professor Exley says waters sold - and easily available - in Britain also contain high levels of silicon.
He said: "Volvic has high levels of silicon, around 20mg/litre. Fiji water has approximately 45mg/litre.
"There is a simple equation you can do to work out the silicon levels in water. If you look at the back of the bottle, it will often state a mg/litre analysis.
"On that list should be 'silica', which is silicon with oxygen. If you divide that number by two you get the approximate value of silicon in that water."
He added that it is more effective to drink the water over a shorter period, such as an hour, rather than sipping it all at once, in order to remove aluminium.
"The major challenge is that we don't have an effective drug for Alzheimer's. This is a real tragedy," Professor Exley said.
"While we know a huge amount, we don't have an effective drug and I think anything that shows some promise should stand a chance of being investigated.
"I think this deserves a chance."
The research is published in the Journal of Alzheimer's Disease Volume 33, No. 2.