I haven't tried it, but I think it's very difficult to do especially if we're talking standing sources where you can't submerge it and scoop water up.

While I'm sure they'll carry a liter, there's no way to measure it. I went from condoms to baby milk bags, going back to condoms would be a step backwards <img src="/images/graemlins/wink.gif" alt="" />

Of course, it's better than nothing