Water And Hygiene · Volume 2
Making Source Water Drinkable — and the Half of It a Filter Cannot Touch
Introduction
The question is how to turn a Michigan lake or stream into water that can go into a Rotopax and be drunk two days later. It splits into two problems that are usually run together and should not be.
The biological problem — bacteria, protozoa, viruses — is solved, cheaply and reliably, by equipment that has existed for decades.
🔴 The chemical problem is not, and in Michigan it is not hypothetical. Algal toxins, PFAS, and legacy mining metals all pass straight through the filter that stops the bugs. A hollow-fibre filter makes water microbiologically safe and tells you nothing about whether it is chemically safe, and the difference is invisible in the bottle.
⭐ And there is a third thing, which almost nobody plans for: filtration makes water safe now. It does not make water that stays safe.
2.1 Filter, purifier, and why the words matter
A filter is a physical sieve. Hollow-fibre membranes at 0.1–0.2 micron catch anything larger than the pore.
Table 1 — Filter, purifier, and why the words matter
| Threat | Size | Caught by a 0.2 µm filter? |
|---|---|---|
| Giardia, Cryptosporidium (protozoan cysts) | 4–15 µm | ✅ easily |
| Bacteria (E. coli, Campylobacter, Salmonella) | 0.5–3 µm | ✅ yes |
| Viruses (norovirus, hepatitis A, rotavirus) | 0.02–0.4 µm | 🔴 no |
| Dissolved chemicals, metals, algal toxins | molecular | 🔴 no — not remotely |
A purifier goes further, either with a much finer membrane (ultrafiltration, around 0.02 micron / 20 nanometres) or with a chemical stage, and claims virus removal as well.
⭐ For remote Michigan surface water, the virus gap is the least important of the three. Waterborne viruses are a human-sewage problem. In a Keweenaw stream well away from habitation they are a low risk, and a plain hollow-fibre filter is defensible. ⚠ Downstream of a campground, a farm, or a town, that reasoning stops applying — and beaver-heavy water is a Giardia problem, which the filter does handle.
2.2 The chemical gap, and why Michigan makes it real
🔴 This is the part that matters most and gets written about least.
Harmful algal blooms. Michigan runs an active HAB programme through EGLE, with a public reporting system at Michigan.gov/HABs and a hotline. Cyanobacteria produce microcystin and related toxins, and the research is consistent and unwelcome: hollow-fibre membranes remove the algal cells well and the dissolved toxins poorly, because a microcystin molecule is orders of magnitude smaller than the pore. Published work shows a submerged hollow-fibre process removing roughly 90 percent of microcystin — which is a long way from safe when the starting concentration is high.
⚠ Boiling does not help either. Cyanotoxins are heat-stable; boiling concentrates them as water evaporates.
🔴 So the rule is avoidance, not treatment: never draw water that has a surface scum, a paint-like or pea-soup appearance, blue-green streaks, or a musty smell — and never in still, warm, nutrient-rich water in late summer, which is exactly when a Michigan inland lake is most likely to bloom. A flowing stream is a far better source than a warm lake, and not only for this reason.
PFAS. Michigan has one of the most extensive PFAS investigation programmes in the country, with surface-water contamination and fish-consumption advisories in multiple watersheds. PFAS passes through a hollow-fibre filter untouched. Activated carbon reduces it; nothing in a backcountry kit eliminates it. ⚠ Check the state’s advisory maps for any watershed that will be a repeated source, rather than treating all remote water as equivalent.
Legacy mining. The Keweenaw’s copper country carries stamp sands and metals in specific, well-documented locations. Again: not a filter problem.
⭐ The mitigation for all three is the same and it is cheap: an activated carbon stage. Carbon adsorbs dissolved organics, many chemicals, and a useful fraction of algal toxins. It is not a guarantee, and it is not a licence to draw from a bloom — but it is the only element in a portable kit that engages with the chemical half of the problem at all.
2.3 The other thing nobody plans for: storage
⭐ A filter produces water that is safe at the moment it comes out. It leaves no residual disinfectant behind.
Put that water in a Rotopax, let it sit warm in a truck bed for three days, and any organism introduced by the container, the funnel, the spout, or your hands has an unchallenged place to grow. The filter is upstream and cannot help.
🔴 Two rules follow, and they are the difference between a system and a filter:
Sanitise the containers, not just once. An unscented household bleach solution, rinsed and air-dried, before the season and after any container has been questionable.
Dose stored water with a residual. A very small quantity of unscented household bleach — the standard emergency guidance is on the order of ⅛ teaspoon (about 8 drops) of 6% sodium hypochlorite per gallon, mixed and left 30 minutes — leaves a free chlorine residual that keeps stored water safe for weeks rather than days. ⚠ Verify the concentration against current EPA/CDC guidance before relying on a number from any single source, including this one, and note that dose is for clear water.
⭐ The elegant version: filter for the bugs and the taste, chlorinate for the storage. The filter removes the cysts chlorine is poor against (Cryptosporidium is notoriously chlorine-resistant); the chlorine covers the days the filter cannot.
2.4 What to actually buy
The gap is point-of-supply treatment, and there are three sensible price points.
The cheap, capable answer — a gravity system, roughly $40–150. A dirty bag hangs in a tree, a clean bag or your Rotopax sits below, and it fills unattended. Platypus GravityWorks 4L runs about 1.75 L/min with a two-bag dirty/clean design; MSR AutoFlow XL carries 10 L at a comparable rate and is built for base camp rather than a backpack; a Sawyer Squeeze with a bucket adapter does the same job for the least money and the most fiddling. ⭐ Gravity is right for a vehicle camp — it is the only option that works while you do something else.
⚠ None of these three includes a carbon stage. Add one downstream, or accept the chemical gap knowingly.
The integrated answer — the LifeSaver Jerrycan 20000UF, roughly $300. It is an 18.5 litre container with an integral pump and tap, an ultrafiltration cartridge rated to 20,000 litres, and — the part that matters here — a replaceable activated carbon disc for chemical and heavy-metal reduction. It removes bacteria to Log 6, viruses to Log 4 and cysts to Log 3 against NSF Protocol 231, and meets NSF P248.
⭐ It is the most capable portable option here — it treats biologically to a higher standard than any hollow-fibre filter, it engages with the chemical question at all, and it is itself the storage container, so filtered water never passes through a questionable funnel.
🔴 But it does not solve the chemical problem, and it is important not to read it that way. Two things temper it, and both come from LifeSaver’s own material:
The carbon disc lasts 500 litres, not 20,000. The ultrafiltration cartridge is good for 20,000 L; the carbon element doing the chemical work is rated to 500 L — one fortieth of it. At this build’s 18–26 gallons a weekend that is five to seven weekends per disc. ⚠ LifeSaver’s guidance is that you know it needs changing “from the taste” — which is a fine indicator for chlorine and staleness and no indicator at all for the toxins you cannot taste.
🔴 And the carbon is tested against chlorine, lead, nickel and cadmium — not against PFAS or cyanotoxins. LifeSaver states plainly that their products “can’t remove dissolved salts and chemical pollutants from water.” No portable filter on this page makes a bloom safe. Source avoidance remains the only real control, and buying the best filter does not buy an exemption from it.
⚠ Three practical costs: it is 8.6 lb dry against about 11 oz for a Platypus; it is hand-pumped rather than gravity, so it is not the hang-it-and-walk-away option; and the carbon disc must be removed for storage, because it is a natural material that decomposes if left damp.
2.5 🔴 Freezing — the failure that does not announce itself
This matters more in Michigan than anything else on this page.
A used filter is wet inside. Water trapped in the hollow fibres freezes, expands, and cracks them — opening gaps that bacteria and protozoa pass straight through. 🔴 The filter still passes water afterwards, and looks and feels completely normal. It simply stops filtering.
⚠ The standard Sawyer Squeeze, Sawyer Mini and Platypus GravityWorks cannot survive freezing. ⭐ The MSR Guardian and the Platypus QuickDraw are engineered to — they are built to accommodate the expansion — and on a truck that camps in Michigan shoulder seasons that is a genuine selection criterion rather than a footnote.
The protocol: once a filter has been used, it never spends a below-freezing night in the truck bed. It comes into the cab, into a sleeping bag, or it is thoroughly dried before storage. If there is any doubt, blow through the clean end — a healthy membrane resists strongly; a cracked one passes air easily.
The expedition answer — a pump purifier such as the MSR Guardian, roughly $400. Self-cleaning, virus-rated, works on genuinely filthy water. Overkill for Michigan, and it is worth saying so.
2.6 How fast, and how long — the two numbers that decide everything
Speed. Gravity systems run at roughly 1.5–1.75 litres per minute, which is about 0.4–0.46 gallons per minute.
Table 2 — How fast, and how long — the two numbers that decide everything
| Volume | Time, unattended |
|---|---|
| 3 gal | ~6–8 min |
| 5 gal | ~11–13 min |
| 10 gal | ~22–25 min |
| 20 gal | ~43–50 min |
⭐ That is far faster than it sounds, because none of it is time you spend. The bag hangs in a tree and fills while camp goes up. Twenty gallons is under an hour of elapsed time and about ninety seconds of attention.
Capacity. This is where the products genuinely differ:
Table 3 — Capacity. This is where the products genuinely differ
| Filter | Rated life | |
|---|---|---|
| Platypus GravityWorks cartridge | 1,500 L (~396 gal) | modest |
| LifeSaver Jerrycan cartridge | 20,000 L (~5,283 gal) | large |
| Sawyer Squeeze | rated 100,000 gal | effectively a lifetime |
2.7 So should everything be filtered?
Yes — and the reason is not the one usually given.
Take a realistic three-day weekend for two people: about 6 gallons of drinking and cooking, plus four showers. At a frugal 3 gallons a shower that is 18 gal/weekend; at a leisurely 5 gallons it is 26.
Table 4 — So should everything be filtered?
| Filter | Weekends at 18 gal | Weekends at 26 gal |
|---|---|---|
| Platypus cartridge | ~22 | ~15 |
| LifeSaver Jerrycan | ~294 | ~203 |
| Sawyer Squeeze | thousands | thousands |
🔴 Filter life is not the binding constraint, and treating it as one leads to the wrong design. Even the modest Platypus cartridge covers roughly two seasons of filtering everything, for a cartridge costing a few tens of dollars — call it two or three dollars a weekend. The high-capacity options make the question disappear entirely.
⭐ What actually limits a hollow-fibre filter is silt, not gallons. Rated capacity assumes clear water. Fine sediment loads the fibres and collapses the flow rate long before the rated volume is reached — on glacial or heavily silted water, badly enough that backflushing every litre is standard advice. Backflushing restores most of it, and a coarse pre-filter prevents most of it.
🔴 So the mitigation is a pre-filter, not rationing. A bandana, a coffee filter, or a proper pre-filter on the intake costs nothing and protects the expensive membrane — and it matters most on exactly the water you would otherwise not have bothered filtering. ⭐ Letting a bucket stand for half an hour before filtering does the same job for free, because silt settles.
2.8 The recommendation
Buy a gravity system now, and buy one with capacity to spare so that filtering everything never has to be rationed. A Sawyer-based gravity setup is the value answer — the cheapest option and the one with the most tolerance for being used freely. A Platypus or MSR is faster and tidier and still covers about two seasons of filtering everything.
Add a coarse pre-filter and use it, especially on anything drawn for washing. It is the difference between a cartridge that reaches its rated life and one that clogs in a season.
Then treat the chemical question on its own merits. If the plan is repeated trips to the same Upper Peninsula lakes, the carbon stage and the integrated storage of the LifeSaver earn their 8.6 lb. If sources are mostly flowing streams well away from agriculture and towns, a gravity filter plus a bleach residual is a defensible system.
🔴 And regardless of what is bought: source selection does more for safety than any filter. Flowing over still. Upstream of camps, not downstream. Never anything with a bloom on it. The best filter in the world is downstream of that decision.
References
- Michigan EGLE — Harmful Algal Blooms programme, public reporting at
Michigan.gov/HABs, Environmental Assistance Center 800-662-9278; MDHHS guidance on avoiding contact with blooms. - Peer-reviewed work on cyanotoxin removal — hollow-fibre and ultrafiltration membranes remove cyanobacterial cells effectively but dissolved microcystin poorly; activated carbon as the practical second stage.
- LifeSaver Jerrycan 20000UF — 18.5 L, 20,000 L cartridge life, integral pump and tap, replaceable activated carbon disc; NSF Protocol 231 log reductions (bacteria Log 6, virus Log 4, cyst Log 3); NSF P248; 3.9 kg dry.
- Platypus GravityWorks 4L (~1.75 L/min), MSR AutoFlow XL (10 L), Sawyer Squeeze — gravity systems that fill a container.
- CDC / EPA emergency disinfection guidance for storing water with a chlorine residual. ⚠ Verify current dosing before relying on it.
- Weight and Balance, this project — why 8.6 lb is a real cost here.
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