by Iori Miller
Water, water everywhere, Nor any drop to drink. Salty water, stinky water, cloudy water … the easiest to fix is the latter. ‘Cloudy, murky, muddy’ … water in a river is generally just suspended clay minerals, typically from muddy river bottoms. It tastes poorly and looks unappealing.
Muddy water is not safe to consume without proper treatment. This is because mud contains many impurities like bacteria, viruses, chemicals, pesticides, heavy metals and other potentially hazardous materials. Yet, before you can filter out the microscopic and dangerous elements, say with a gravity filter, the suspended solids causing the murkiness must first be removed so they don’t ‘clog’ up the filter and immediately render it completely useless.
For thousands of years, people have used Aluminum Sulfate, commonly known as “Alum,” as a water clarifier. Ancient Egyptian hieroglyphics describe the use of “aluminum earth” and first century Greek and Chinese documents tell of mining and use of Alum for clearing water. By the 16th century, Alum was in widespread use across England, for treating municipal water supplies. Its use continues to this day in water treatment facilities, as a ‘flocculant’ to clear turbid water, and to some extent, remove phosphates, pathogens and other undesirable particles.
Aluminum Sulfate is an ionic compound with high solubility. Often clay particles suspended in solution build up charges on their surfaces due to friction, and this attracts ions to their surfaces. They further attract more particles, and the result are clot-like masses with less buoyancy. This action is called ‘flocculation’, and it is both a physical and chemical reaction that is promoted when Alum (the flocculant) is mixed into solution.
There is an urban myth that Aluminum in any amount is toxic or causes a variety of ailments. The US FDA has determined that aluminum used in food additives is generally safe. Alum is not considered a carcinogen by the International Agency for Research on Cancer (IARC), and the LD50 of Alum is >5g per kg of water.
For a canoeist or hiker, the simplest approach for clearing cloudy water is to let it settle and filter it through a clean cloth, towel, or coffee filter. Then to purify, bring the water to a rolling boil for at least a few minutes. If you wish to be more thorough, you can use a flocculant (Alum) first to remove the murky components, and then a standard gravity filter to purify.
The simplest approach for treating cloudy water is to prepare a ‘flocculant solution’ by mixing some powdered Alum in a 1L Nalgene, and shake it until the Alum is dissolved. After a prescribed portion of this solution is added to a 5 gallon pail of muddy river water, it is stirred thoroughly and then let to sit undisturbed for half an hour.
Specifically:
- 1.5 tablespoons of alum powder are added to 1 Liter of clean water in a widemouth Nalgene container and shaken thoroughly.
- Pour 4 Nalgene capfuls into a 5 gallon pail of the river water. Stir vigorously for half a minute.
- Let the pail sit for 30 minutes, undisturbed.
- After, you should notice the water has cleared, with a ‘sludgy’ looking layer sitting on the bottom of the pail. Now you should carefully decant* the upper, clear, portion of water in the pail and run it through a gravity filter to further purify it.
* I find the best approach for this is to use some of the tubing from my ‘Platypus Water filter’ and use it to siphon off the upper clear settled water into a separate, clean, container (for me, the upper ‘dirty water’ bag of my gravity filter).
==> How to Treat Silty River Water With Alum: You Tube – ‘The Southwest Backpacker’
Note:
- Adding 1.5 tbsp of Alum to 1.0 L, is 45 g/L.
- Adding 4 Nalgene capfuls of this to 19 L (5 gal) of dirty water in a pail is like 2.0 gram/pail?
- You would have to drink more than 2 entire pails (10+ gal) in one sitting to get close to the LD50 of >5g per kg of Alum in water.
- You would have to drink more than 2 entire pails (10+ gal) in one sitting to get close to the LD50 of >5g per kg of Alum in water.
- This method of water settling is safe.
- Remember that Alum is a common additive in pickling salts.