Susan ... I was thinking a bit more about the sand filter. A couple of things came to mind. The first is that you would need to have clean sand. If the sand has any salt or soluble minerals, they will get into the water. This is probably why the folks in Japan are not using this method in the tsunami zones. All the local dirt and sand has been contaminated with seawater.

The second thing is that some of your water will stay in the sand - the sand will remain wet. So you will lose some water when you use this technique. If you have a major source of water, then this may not matter at all. But if you have a very limited water supply, then you may not want to lose some to the filter. In that case, it may make more sense to filter impurities (dirt, algae) with some layers of cloth.

Pete #2