A weed that spreads rapidly through ponds, lakes and rivers could provide a cheap yet effective way of removing arsenic from drinking water.

A research team at UK's De Montfort University, led by Parvez Haris, has found a powder made from the dried roots of water hyacinth (Eichhornia crassipes) removed nearly all the arsenic from a tap water sample. Within one hour of adding the powder to the water, the arsenic level dropped from 200 parts per billion (ppb) to below the World Health Organisation's safety limit of 10 ppb (Journal of Environmental Monitoring April 2005, Vol 7, No 4). Andrew A Meharg, a biogeochemist at UK's University of Aberdeen, says the approach could be an advance over methods based on chemicals, because many affected households have ponds or seasonally flooded fields where water hyacinth could grow. But the method would produce large quantities of contaminated root powder that would need to be safely disposed, he cautions.