IN her letter (February 26) Dr. Karen Cunningham states that ''Dasani is . . . purified using a state-of-the-art purification process called reverse osmosis''. My understanding of the term ''state-of-the-art'' means that the very, very latest technology is being used. In your article of March 2, Row as Coca-Cola sells bottles of purified tap water, you seem to confirm this by saying ''reverse osmosis is described as a technique perfected by Nasa to purify fluids in spacecraft''. There is absolutely nothing new about reverse osmosis. To my knowledge it has been used in desert conditions to desalinate water for moer than three decades and probably a lot longer than that.

Jim Bullock,

9 Allanvale, Dunlop, Ayrshire.