The extra water helps flush bacteria from the bladder, and reduces the possibility of the bacteria attaching to the cells that line the urinary tract, which happens when a UTI develops.
While it sounds logical, nobody has really tested the idea before, say researchers from the University of Miami school of medicine.
They got together a group of 140 women who had suffered at least three UTIs in the past year, and whose fluid intakes were quite low. Half carried on as normal, and the rest were told to drink an additional 1.5 litres of water a day, which is roughly equivalent to three 16-ounce glasses.
With all the other drinks the women would consume in a day, their fluid intake rose to 2.8 litres, while the non-drinkers were still drinking around 1.2 litres every day.
After a year, the women who didn't drink extra fluids reported having just over three UTIs in those 12 months, while the extra-fluid group suffered around 1.6 UTIs on average, a 48 per cent reduction.
It's estimated that up to 60 per cent of women will suffer at least one UTI in their lifetime, and 25 per cent of these will have a repeat infection.