Find a container, preferably an empty can or a large plastic bottle. Cut off the neck end of the bottle with a knife. Use your knife to punch about 10 small holes in the bottom of the container.
Fill the bottom 2 inches of your container with pebbles or small stones. You should be able to find these on the lake shore. Alternatively, use non-poisonous grass or cotton material. Clean cotton underwear makes a good filter.
Add around 2 inches of gravel or grit. Get this from the lake shore.
Take charcoal from your campfire and crush it into small, gravel-sized pieces. Add it to the container. The charcoal will remove bacteria from the lake water.
Fill the rest of the container with sand. There should be plenty of sand beside the lake.
Collect water from the lake with a second container or watertight bag.
Place a third container under your sand filter. Prop the sand filter upright with a stick or rock. Pour water through the sand filter until it has all drained through to the container.
Check that the water is clear. If not, pour it through the sand filter again.
