Anymore I use an activated charcoal filter and boil water. If I were to use a chemical treatment I'd filter the water after treating it with an activated charcoal filter.

The charcoal filters I use are made by Britta for their "Squeeze Bottle". They're small and light. I use them in collapsible bottles made by Enfamil. There are larger collapsible bottles available. Together they're light and easy to pack.

When you're kayaking just strap a clear plastic jug of water to the bow of the boat where it's directly in the sun all day. That will sterilize it as good as any chemical treatment. If it's cloudy water filter it with an activated charcoal filter before you set it in the sun.