I will disagree with you both on the priority for water purification, particularly for a 72 hour kit. Within 2 minutes of my doorstep I have Lake Washington - you'd think I have plenty of water in a pinch. While hiking there are not many places this side of the Cascades where you are very distant from a potable water source. However, after an earthquake, Lake Washington will be fouled by a damaged oil pipeline, and also likely by sewage line ruptures - sewer mainline for my neighborhood crosses the Mercer Slough a mile south of here, approximately at the epicenter of the Seattle Fault zone. If that's the case, drinking the water could create bigger issues than giardia. As for purifying water while hiking, the size of MicroPur tablets is miniscule, and if you have had giardia (I have not) you wouldn't want it facing your future, even if your focus was only on the next 72 hours - because the diarrhea etc is prolonged. Potable water and a mechanism to purify it is an essential IMO.