I wouldn't necessarily call it lightweight- though it isn't heavier than most purifiers.

I got tired of pumping and pumping and pumping. And I I got tired of using a couple of the name brand filters that would get clogged before we had pumped enough water for the people I was with - usually on a scout backpacking trip. So I ended up buying a UV light purifier. 60-90 seconds depending on the size of the bottle, and you're done.

You want to have running water - because it doesn't filter. So if you are filling your bottle from a dirty water source it is still going to be dirty.

The lightest weight option is probably the little pills. But then you get a little flavor/aftertaste. So you'll want some flavor to add in.