This is an addendum to my run report from Monday for my 25 mile run along the C&O Canal.
I left out one key detail in my haste to post, but actually the delay has provided time to better analyze results. My plan was to resupply with water and food at my car somewhere in the middle of the run. That is, I first ran downstream and back, pausing at my car, then headed upstream and back. However, in the middle of my initial downstream leg I opted to lengthen that leg to about 2/3 of the run. That meant, even in cold weather, that I ran out of water.
I knew that I would run out of water by lengthening my first segment, and had planned for that contingency--by carrying a small bottle of liquid bleach. This is a recycled infant's liquid Tylenol bottle with a dropper. A couple years ago on the Ultralist I had read a post from a university chemistry professor stating that 7 drops of bleach will purify a standard 22 oz water bottle in about 20 minutes.
I've previously used this technique perhaps half a dozen times without any adverse consequences. On Monday the Potomac River was high and brown from recent rains. I climbed down to the riverbank from the canal towpath, filled a bottle, and added the bleach. I used 10 drops due to the murkiness of the water, which was the color of very weak coffee. Twenty minutes later I happily drank the water, which really did not taste bad, either from the bleach or funky water. Now 3 days later I still have no adverse consequences.
Your mileage may vary. LEGAL DISCLAIMER: I am not a water purification expert and therefore if you try this technique you do so at your own risk. But it certainly provides an extremely useful option for water resupply while out on long runs.