The immediate answer to this question is that washing hands with water and soap saves lives. Washing hands with water and soap can reduce diarhoeal incidence by one-third.
Diarrhoea still claims two million lives every year! 
WASH is also the acronym for Water Supply, Sanitation and Hygiene; the combination of which can reduce diarrheoeal disease even more than by washing hands alone. Hence, WASH 'for life', as WASH services provide and preserve life.
Fortunately there are many relief and development actors, providing WASH services to populations in distress; distress from living in or having to flee a conflict zone, being a refugees or internally displaced; from a disaster or the effects of climate change, droughts, cyclones and floods; or from living in constant poverty. 
WASH for life is a global consulting consortium whose mission is to support those relief and development actors to design and deliver appropriate and high-quality WASH programs. "We help you help better!"
Our vision is a world where the WASH needs and rights of people affected by crisis are being addressed fully, timely and appropriately.