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Filtering Silty Water

Is it possible to process silty water in the back country and make it safe enough to drink?

Four of us are going to kayak Stillwater Canyon on the Green River in Utah soon. A 5 day, 52 mile kayak trip on one of the siltiest rivers in the country. It will be difficult to carry sufficient drinking water in a small kayak for the entire trip. Assuming that one should always have 1 gallon per person per day, and a gallon of water weighs 8.33 pounds, that is over 40 pounds and tons of space!

Confluence of the Green River (left) and the Colorado River (right) in Canyonlands National Park.  You can see how silty the Green River is compared to the Colorado.


Most of our google searches suggested just carrying the necessary water. Any of the Sawyer filters (or other brands for that matter) would clog horribly the first day. The solids in that river are full of salts, clay and other nastiness. One of our group thought to ask the outfitter providing transport to and from it was possible to somehow filter that incredibly silty water. Sure enough, they had a method. I certainly am not willing to risk my life on something not tried in the safety of home first. So here is how a home experiment in clarifying water for filtering went.

The Premise

Alum or Aluminum Sulfate, when added to water, produces a water treatment process call flocculation.  Without going into details, this process uses the Alum to bind with particles floating in the water and then they sink the bottom of the container.  Alum is using in pickling and canning and is available at the grocery story or on Amazon.  We are going to use alum to replicate a water treatment facility at home prior to trying it out in the wilds of Utah.

The Experiment

In order to empirically study how to de-silt river water, one needs silty river water. Since the Green River is nearly 7 hours away, I decided that would not work. The Colorado River below Hoover Dam, while much nearer to home is nearly perfectly clear. I decided to go hike the Paria River narrows (only 3 hours from home) known for it’s silty water and significant amounts of sediment. The Paria River runs from it’s starting point in Escalante Grand Staircase National Monument through Buckskin Gulch and finally to it’s end point at Lee’s Ferry and the Colorado River.

Paria River south of White House Trailhead

The Paria River is known for having silty unfilterable water. Perfect for this experiment. I used a collapsible clear water bottle to collect the silty water.

Silty Water

After letting the water sit undisturbed for 24 hours, it is certainly clearer, but not really clear. We need a way to get the solids out of the water without taking too much time and without fancy expensive filtration systems.

Settled Silty Water


Control sample (not treated), treated sample, jar of alum and little water bottle with dissolved alum.

Time to experiment!

Dissolve a teaspoon of dissolved alum into the the glass to be treated and stir for 2 minutes.

Stir alum solution for 2 minutes!
15 minutes in, you can definitely see the difference.
The solids are visibly sinking
30 minutes
One hour with the addition of a coffee filtered water that looks something between the two. Please ignore my science lab partner.
After 3 hours all three samples have good settlement. Both the treated and the coffee filtered and treated waters look clear enough to filter with a gravity filter.
Sediment is still dropping
After 12 hours, this water is as clear as it is going to get.


Most of the settlement occurred during the first couple of hours and running the water through a basic coffee filter and then adding the alum worked best.  

Now the water can be filtered and treated for the floaties you cannot see. It turns out that that the taste of alum is extremely bitter and astringent.