Using Alum in the backcountry…calling David Thomas and other science-minded folk

[Travis Leanna]

If all goes according to plan, I'll be spending about 5 days in a packraft along the Little Missouri River this summer. From what I know, the silty river water will render a filter useless in short order. I'd like to know, as specifically as possible, what the best technique is to use alum in turbid water. Here's my plan:

Gather water

---

>add alum

---

>let settle

---

>skim off crap/decant after flocculation—->run water through a prefilter like the MSR Siltstopper—->run the water through final filtering in a Sawyer inline.

Is there a more efficient or quicker way?

How much alum is needed?

Is grocery store grade alum all I need?

Would simply pre filtering through a bio fuel filter work just as well?

Thanks!

[David Thomas]

Travis,

Grocery store alum is fine.

There is no cheaper, more effective way than alum if you have 30-40 minutes to let it settle. It should be the first thing you do as you make camp is to set up your settling pots/buckets so later in the evening and the next morning, you can process it. For overnight, you may be able to skip the alum (do one test bucket the first night). But if you want clear water in 30-40 minutes, use the alum.

Use about 1 gram per 20 liters / 5 gallons. An easy way to measure it is to have a "pre-mix" bottle with an ounce of alum ("shaken, not stirred") in a liter of water. Then a 1/30 of the bottle (1-2 capfuls) will be one gram.

Use more pots/buckets so you have no temptation to drain off the bottom 1/4 of the volume. You'll quickly find that bumping or kicking a pot spoils the results. You'll also develop a very smooth technique for decanting off the clear water. taller buckets make this easier to do without disturbing the sediments on the bottom.

You're exactly right that you want to skim the scum. Do that early and let the sediment resettle. Or skim the scum VERY gentle. Some river water has very little scum – no floaters, all sinkers. You'll find out the first day.

5-gallon buckets are wonderous things – cheap, fast, large capacity. But you're in a pack raft? So maybe you don't have a lot of room?

Very compact, light, and free alternative to 5-gallon buckets:

Go dumpster diving at the recycling center. Score LOTS of 1-gallon milk jugs. Use sturdy scissors to cut off the top half (never use a razor if you can possibly use scissors and you'll reduce trips to the ER). Play with the height – 3" high nest very well and make very cheap and light serving bowls/plates. 5-6" high hold more water each (duh) but don't nest as well. But you'd a lot of such 1/2 gallon "bowls" to equal each 5-gallon bucket.

A micro-civil-engineering project ("the kitchen sink"). The ultimate compact water container is a hole in the sand lined with a tarp (or, in a pinch, a WP parka, but its going to get muddy). Ferry water to the "sink", add alum, stir, and decant off the clear water 30 minutes later. 2' x 2' x 1' = 30 gallons. Dig less soil by piling the spoils up as a lip for more height. Avoid digging through tree roots – they go a LONG way in the desert.

A mini-mechanical-engineering project: I've been know to bring ten 24" x 24" plywood panels, secured together with 2" nylon webbing, and then lining it with a tarp. A 6-foot-diameter hot tub holds 8-10 naked college students and each human is 15-20 gallons of water you DON'T have to schlep or heat up. Then there's heating the water, but that's a whole other thread.

But don't short yourself on water storage. If you aren't packing away enough treated water the night before, stop again mid day and let another batch settle during lunch. It is appropriate, IMO, on a desert trip, to frequently ask companions when they last peed. If the answer is more than 2 hours ago, they HAVE to drink a full liter then and there with another one to be consumed, perhaps more slowly in the next hour or two. Women usually do less stupid stuff than men do, but some will minimize fluid intake to avoid frequent potty breaks. That's not good.

The work of pumping through filters really sucks in a hot environment (we did a GCNP private raft trip a few years ago). I'd do some UV and iodine or chlorine AFTER the flocculation in a clean container without the sediment.

But if you are filtering, I think you'll be getting water so clear that you needn't bother with the pre-filter.

-David

Edited to add: label the pre-mix bottle. Wrap it in red tape or something. You don't want someone drinking all the alum solution. While at the recycling center, I'll offer grab various HPDE (my favorite plastic) bottles and run them through the dishwasher at home. Something like a hydrogen peroxide bottle is totally food-grade, has a secure lid, and is pretty sturdy (less like to get punctured), but no one will mistake it fro a water bottle.

[Greg Mihalik]

"Would simply pre filtering through a bio fuel filter work just as well?"

Up in BWCA you can clog a filter fast, in optically clear water, due to a particular algae. It is to small to pre-filter but big enough to clog a PointOne. I have had the same experience with fine sediments. Pre-filtering won't make much of a difference if the stuff is under 5 microns.

You can get a pre-filter that will take it out. But you will need a lot of them because…they will clog.

Just take the giant syringe so you can back-flush. As designed. It works well. Bulky, but light.

[Kevin Babione]

My river experiences have been in canoes rather than packrafts, but there was no way I was going to drink the water from the river I was canoeing. What we did was to get our water from the many streams that fed into the river. Sometimes we'd have to hike a little upstream to get to where it was flowing freely, but not very far. We didn't have to worry about any portages over our 5-day trips, so we'd try to camp near one of the feeder streams and prep all the water we'd need until the next campsite.

I don't know anything about the Little Missouri River, but from what you've described you'd be much better off getting your water from other sources.

[David Thomas]

Kevin makes the excellent point that side canyons and streams can be a lot less sediment-filled than the main channel. It saved us the work of cleaning the large filter so often – those times we could get water from a clear side stream to the Colorado.

[Travis Leanna]

Thanks all of your for very helpful answers; and David, spot on with a fabulously thorough and complete post. Exactly what I was looking for.

Greg, I know what you mean about optically clear water that clogs filters. I run into that once in a while in WI. Frustrating stuff.

Kevin, yeah, any time I can find clearer water, I'll be sure to do so. A lot will have to do with the rainfall in the weeks and days leading up to the trip. I have a map on order and will be studying it for possible water sources, including drainages, wells, and troughs.

I'm coupling this packrafting section with about 90 miles of hiking trail along the Maah Daah Hey trail. There are potable water sources 18-25 miles apart, so I'll have access to *some* clean water, but I need to have the means to quickly gather water if conditions warrant it. Given the route of the river and trail, those water sources may not be accessible during my time on the river.

Even in a drought year along the Grand Enchantment Trail, I was always able to find water at acceptable intervals, but when chances are water may be scarce or filter unfriendly, I'd rather be armed with the know-how and tools to secure good, safe water.

[Travis Leanna]

Right now I plan on getting the Sea to Summit 10L bucket. With care it's supposed to be free standing and weighs 2.8 ounces. In this I'll let my alum water settle.

Without bringing a heavy pump filter, does anyone have any ideas on the best way to get water out of the bucket without disturbing the sediment at the bottom?

Gentle scooping with a small cup?

[David Thomas]

Very nice weight on a 2.5 gallon bucket!

A short length (3-4 feet) of 1/2" tubing could siphon it out. You prime the siphon by mouth (but they tell you never to do that in chemistry lab) or just submerge most of it, cover the dry end with thumb and pull it mostly back out of the water so some of the filled tubing is below the level of the water.

Vinyl tubing is readily available in cut lengths and cheap enough, but not light and not quite as stiff as you'd like. It'll work, but polyethylene (the milky white plastic HPDE of a gallon milk jug) will work better and be lighter. But sometimes it isn't sold by the foot and you have to buy 10, 15, 20 or 250 feet depending on diameter. Again, I know 1/2" will let you move about 3-4 gallons per minute but anything between 1/4 and 3/4" would work.

Bring some manner of clothespin or binder clip (sized for the tubing) so you can clip it to the side of the bucket – especially for small diameter tubing which might take a few minutes to decent off the clear water.

Garden hose is 5/8" – you could cut 4 feet off of an old one.

If you can't find the HDPE or a reasonable length of it or are in the sticks, PM my and I'll send you a length. It's one of many stock items in my shop.

[Travis Leanna]

David, I had considered siphoning it, but I questioned the practicality of it. Meaning, wouldn't the bucket need to be higher than the resevoir I'm filling? I suppose I could hold it up, but at the cost of possibly disturbing the bottom when picking it up. I could be gentle and careful, but the bucket being soft sided and bottomed, I'm not sure. I might have to try it at home first.

[David Thomas]

Absolutely, the source bucket would have to be higher than the receiving container to siphon it. Could you usually hang it from a tree (just a few feet up), a rock, or a slight rise? The shady side of a tree would offer height and a cool spot. In a pinch, one person could slowly lift it and hold it for siphoning.

This is gilding the lily, but if you had a bag of just the right wicking/water-resistance, you could have colder, settled water. I'm thinking of the old, canvas "desert water bags" you hung off your front car grill and the evaporative cooling in hot, dry climates kept the wet canvas bag cool (back in the days before A/C). I actually remembering borrowing our grandfather's for a Death Valley Owen's Valley trip circa 1972 as my family's car didn't have A/C.

I'm imagining a Walmart/Safeway reusable shopping bag (69 cents) which is too porous, lined with something more porous than Tyvek (just a square yard of it).

A LL Bean canvas tote bag would work as it, but isn't cheap or light. Maybe a cheaper, knock-off cotton tote bag, maybe with tighter stitching on the seams. Or maybe the seams would be okay – I think part of the magic is that cotton fibers swell when wet, so imperfect seams or needle holes seal themselves off.

[Travis Leanna]

Hanging may or may not be an option in the badlands, but considering ill be using the bucket while along the river, there should be some stout branches of trees growing in the valley.

Hmmmm, this will be fun playing with!

[Travis Leanna]

I was able to pick up the bucket and tubing today. I ended up getting 3/8" inside diameter vinyl tubing because the HPDE stuff, although lighter, was very stiff. It probably would have been much harder to control as it curved up and over the floppy lip of that bucket.

The bucket surely holds 10 liters and stands very solidly by itself (for a non-rigid container). I was able to siphon at a rate of about 5 liters in 2, maybe 3 minutes, but I wasn't timing it.

I think this should work well for extracting clearer water after flocculation (my wife says that sounds like a dirty word.)

[Author]

Posts