Add another voice to the Pur-Katadyn Hiker. I prefer getting the bits strained out of the water before I drink it. If just boiling or using a chemical purifier, sure that's fine to kill the bateria/virus but the added psychological benefit of having visually and tastefully clean water is worth every gram of weight to the people I hike with.

I've used the Hiker to clear water from heavy algaed coverd ponds, milky glacial melt water and running stream water. They've all benefited from the filter.

Chemicals are good in a pinch but the water as some extraneous taste. Even boiled water can taste funny after being used to clean cold water.