No one wants to haul bottles of water up a 4,000-foot trail--but you absolutely need to stay hydrated. Grayl's filter bottles offer an ideal solution. Parched after reaching the Fluhalp hut outside Zermatt, Switzerland, I immediately filled my 24-ounce Grayl bottle ($90) at the fountain outside. Only later when my head cleared did I notice the "Do Not Drink" warning above the faucet. Thankfully, the bottle's filter kept me safe from any pathogens, bacteria, or heavy metals.