UK health authorities are trying to find out whether home water-softeners could help fight eczema.
The Department of Health-backed study will also look at the differing effects of hard and soft water on the condition which causes dry and itchy skin.
Eczema has been reported to be more common in hard-water areas but it is not understood why that might be.
One mother who has taken part in the research said she had seen a "dramatic improvement" in her son's condition.
It typically occurs on the face, neck, and the insides of the elbows, knees, and ankles.
In infants, it is usually seen on the forehead, cheeks, forearms, legs, scalp, and neck.
The study, which began in 2007 and will run until this summer, is recruiting children aged six months to 16 years with moderate to severe eczema.
Eight research centres in Portsmouth, Boston, Lincoln, Nottingham, Leicester, Cambridge, Newport on the Isle of Wight and London are involved.
Just over 230 children have already taken part, but the researchers are looking for another 80.
The children, or their parents, will be asked to complete a daily diary to record eczema symptoms and will be issued with a small computerised wristband to monitor their level of night-scratching while they are asleep.
The families have the water softener for 12 weeks, then it is taken away from another four to see if there is any change.