OK - show me someone who's done a thruhike with just a Lifestraw.
Sorry, but not bringing a bottle or a flask because of weight is known as Stupid Light. Yeah, you could probably do it, but it's stupid to do. Another example is using a keychain light as your only light. You could do it, but it's stupid to do, and if you end up in an emergency situation, you're going to get little sympathy for the team of rescuers that save your stupid light butt. These ideas are what happens when you are sitting and looking at a spreadsheet of gear weights in a far larger proportion then actually being out and seeing what actually works.
