Stuck in the (urban) wilderness without clean water? DIY Life has a short video guide on how to purify water. You can make use of materials that will probably be able to find around you.
What you need:
1. Empty plastic bottle
3. Matches or other firestarting equipment
4. Wood (or other combustible material)
You might want to pre-filter the water using a piece of cloth to get rid of the larger particles.
[ via DIY Life ]