"What we've found by bringing together all of the evidence for the first time is that there is a suggestion that these interventions improve the growth of children and that's very important," he told BBC News.
"This is the first time really that evidence has been provided to support the provision of water sanitation and hygiene interventions to improve growth."
He said there is a clear link between a child drinking dirty water, getting diarrhoea and having poor growth, because repeated illnesses in early childhood can impair growth.