Keeping clean when trekking or when you're out in the woods can be a problem but here's a clever idea:

As the website says

Turn 1 litre of clean water into 10 litres of washing time
Bottleshower™ provides emergency washing and showering from a bottle for refugees, disaster victims and aid teams who rely on water distributed in plastic drinking bottles.
See the benefits of Bottleshower™ by watching our video below.
http://www.bottleshower.com/