Gear Selection: Water treatment for the GDT 2021

Our water filter stopped flowing prematurely this season while on the SCT, forcing us to use chemical treatment on trail. As a result we started reconsidering our water treatment system.

We have since cleaned the filter and it flows again, but we are still going ahead with chemical treatment on the GDT for 2021.

Current System

Years ago we chose to go with a water bladder system to encourage us to drink while hiking. We generally don’t stop for water breaks and hike all day as hard as we can, so having any encouragement to stay hydrated is helpful.

Our system was to connect a gravity works filter to our bladders so we could filter and fill the bladder while it’s in our packs while we are stopped for lunch.

We also each carry a 1L water bottle to use in the tent and to drink coffee, Gatorade or meal supplements out of.

When hiking the GDT in 2018 our gravity filter held up the entire trip after many years of service but eventually started clogging near the end. Around Moose River it really started to clog – that is a very silty stretch.

Our replacement was a BeFree filter. It is a little lighter than the gravity works filter and packs a little smaller. It is a little more difficult to use; the bag is a little more challenging to hold when full while threading the cap on and the cap has the filter integrated (which you can’t touch or get dirty).

This worked for roughly 1.5 seasons. We went to use it this year and it was a trickle. So we had to use chemical treatment on our SCT shakedown hike.

Our Selection

We looked at our water system weight and figured since we have been using chemical treatment we might as well use it on the GDT and leave the filter at home.

Chemical & Amount

We chose chlorine treatment, using household bleach, as our chemical.

Iodine treatment is not recommended for extended periods and is not recommended for use with infants or pregnant women. So we opted not to go with iodine as our primary system. We do carry iodine tablets as a backup but we will not use iodine treatment for water we give Toothless.

There are questions about chlorine also hurting gut bacteria. Some places recommended boiling water (to boil off chlorine) before giving to children under 12 months. With Toothless, we plan on boiling water or letting chlorine treated water sit out for a few hours to let the chlorine evaporate off. He can also breastfeed to get hydrated as well.

Chlorine bleach is recommended by our province in quantities of 0.1 mL of bleach /L of water.

The US CDC lists out the required treatment (quantity and time) for different pathogens and viruses. Chlorine can kill most pathogens; a couple pathogens are resistant against chlorine. Filters are, from our understanding, small enough to remove larger pathogens but not small enough to remove viruses. So using a single method leaves gaps in effectiveness.

The density of 5% chlorine is 1.093 g/mL.

In general, from the CDC tables above, chlorine in quantities of 2 mg/L (0.002 g/L or 0.002 mL/L) is sufficient to kill most pathogens if left for 30 minutes. It is even more effective if left for an hour. Chlorine concentration of 100 mg/L (0.1 g/L or 0.1 mL/L) is required at very long times to inactive the entire list of pathogens and viruses on the CDC website with varying levels of success and resistance.

We purchased a 15 mL dropper from Litesmith. I verified the mass of chlorine bleach per drop using our kitchen scale. There is approximately 0.034 g/ drop.

So three (3) drops of bleach per liter of water will provide the recommended concentration of 0.1 g/L, assuming a 5% concentration.

The dropper bottle can hold 16 grams (15 mL) and if we assume that between Natasha and I we need to treat 4 L of water per day the dropper should last 41 days. On our usual pace this would be the entire GDT, but this year with Toothless at a slower pace this is about 2/3 of the GDT. We will pack two (2) other full droppers to be conservative, so we never will have to worry about water consumption.


Organic matter can react with chlorine and cause some not good compounds. So we have chosen to prefilter our water.

For convenience we have purchased a funnel from Hennessy Hammocks and will use that. The funnel has a coarse metal mesh and screws into a pop bottle. The mesh can catch large debris.

For finer debris a bandanna over top works well. The funnel holds water and even if the bandanna flows slowly, the funnel keeps it flowing into the bottle.

The funnel also does a good job of catching water, including anything fast moving but low depth. The funnel also is a good handle to keep the bottle from slipping out of your hands while filling.

The funnel is 10 g, and seems well made.

Final System

We will move to each carry two 1 L water bottles, and we will have one funnel and one dropper. The water bottles we carry are similar to a Smart water bottle, but of a different brand. Our LighterPack lists a Gatorade bottle which is heavier, but we only carry Gatorade bottles for day hikes and switch to lighter Smart water bottles for longer hikes.

ItemMass (g)
Hennesey Hammocks Funnel10
1 L Smart water bottles (or similar) x 2 for Kyle~70 (2*35)
1 L Smart water bottles (or similar) x 2 for Kyle ~70 (2*35)
Dropper bottle6
15 mL of chlorine bleach16.4

This eliminates a lot of weight from our pack and eliminates some of the volume the water takes inside the pack. With Toothless’s gear, the added accessible internal pack volume is useful.

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