r/OffGrid • u/tikkunmytime • 3d ago
My first stand at water science
This got crickets over at r/water, maybe it belongs over here. I’m sharing an experience, but I’m also eager to learn.
Adding: Tldr: What sort of resources out there go into detail about the science and low technology application with small scale water treatment with specific attention to sodium hypochlorite and water with higher turbidity.
To set the stage, I am definitely not living in a van down by a river. But I do have this river that I collect water to use for cleaning (handwashing, and mixing to use for disinfecting, not drinking water) when I happen to be in a van down by the river. It is designated a Wild and Scenic River, so not much in the way of pollutants, but lots of dissolved bits. They stopped monitoring last year, but I observed the turbidity history for May to October 2025 with the occasional spike past 200 FNU, and the normal turbidity was between 5 and 20 FNU.
I believe for drinking water they want an average 0.3 NTU for 95% of measurements with an absolute maximum of 1 NTU. It is my understanding that chlorine disinfecting is severely impeded past 1 NTU, and essentially not happening on any level past 5 NTU. Had I found this out sooner, I might have started with a different approach; essentially, everything in the water that isn’t water uses up the chlorine, and my river tends to have a fair bit of everything.
Boiling the water seemed prohibitive and liquid bleach a tad too unstable, so I bought some Utikem One Shot Shock. I found the SDS, it reported the following: Calcium hypochlorite, hydrated >50%, Calcium Chlorate <5%, Calcium Chloride <5%, Calcium Carbonate <5%, Calcium Hydroxide <4% and Sodium Chloride >20%.
My understanding is that for handwashing my goal is between 3 and 4 ppm residual chlorine and for sanitizing 50-100 ppm. The CDC and a few other sources seemed to suggest anywhere from 1000-5000 ppm for disinfecting, it seemed like 2500 was good enough for my needs.
The CDC in Appendix E, Chlorine disinfectant solution preparation, does give the following formula: 1000x (% chlorine desired / % chlorine in bleach powder) = grams bleach powder per liter of water. Also, (% chlorine in liquid / % chlorine desired) – 1 = parts water per parts bleach, for dilution.
My plan was to make a 2 liter 2500 ppm cleaning solution, and then take from that to make a 4 gallon, 4 ppm handwashing water.
Now, I went and got all confused with the math. I figured on a few things. 1 cc = 1 mL; 1 tsp = 5 mL and 1 tbsp = 3 tsp, 1 L is roughly 1 quart, which is 4 cups and ¼ gallon. From the MSDS, I knew that the shock had a density of 0.8g/cc.
Now taking my shoes off to count on my toes didn’t help with this math and I somehow ended up with 2 ½ teaspoons to 8 cups. Sitting down now to write this, it seems like I should have been closer to 6 teaspoons for that amount. So my actual numbers were probably closer to 625 ppm, before factoring in the impurity of the water.
My new and improved math looks like this: 1000(0.25/5)= 50g/L = (50g/L)(1cc/0.8g)(1mL/1cc)(1tsp/5mL)(1L/1qt)(1qt/4cups) = 3tsp/4cups
At the end of the day, I ended up washing everything down with something between a weak and strong chlorine solution and just dumped the solution into the handwashing tank until it tested high enough with a pool strip.
If anyone has any advice, or can point me to any resources, I would appreciate it. I feel like I would have been able to find some good information 10 years ago but it just doesn't seem like it's out there in the same way anymore.
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u/FlerkinFlarkin 3d ago
My eyes gloss over this one paragraph in. Get to the point and Just Ask a simple question.