Lightcap has unveiled a solar powered cap for your water bottle.
Their website lists a price of $24.95 says for the :
The solar power unit is totally sealed; in fact, it is molded in from the top (outside) of the cap so thereÃ¢â‚¬â„¢s no possible contact with the contents of the bottle. ThereÃ¢â‚¬â„¢s also a handy waterproof switch on the cap that lets you change from the white LED (bright), to red (preserves your night vision), or turn it off completely. You can leave the red light on all night (minimal energy draw) so you can easily find the bottle; then switch it to white if you need a light!
A fully charged cap is expected to last 8 hours.
Comments on the Treehugger Blog note the ingredients are toxic but they are sealed.