One of the tips I picked up in the Marine Corps was how to carry 2 water purification tablets for an emergency. Typically we would just keep the small bottle or individual wrapped ones inside our first aid kits. During a training evolution at the Marine Corps Mountain Warfare Training Center, the instructors would occasionally share survival tips and tricks.
When I was in, we didn’t have access to any fancy water filtration systems like they do now. Our options were to boil the water or use purification tablets. Boiling usually wasn’t allowed for tactical reasons.
One of the instructors suggested we take two water purification tabs and duct tape them to the side of our USGI canteen. This way we always have a few tabs available as we are filling our canteens from a lake or stream. Plus if we had to dump our packs during an E&E (escape & evasion) scenario, we would always have a way to purify our water on the move.
In the above picture, I took two pre-packaged water purification tabs and duct taped them to the side of my canteen.