Pre-Filtering and the Camp Water Scheme — Good, Better, Best

Introduction

The previous volume established that silt, not gallons, is what kills a membrane. This one is about keeping silt away from it, and about the sequence the whole water operation should follow so that clean and dirty never meet.

⭐ The single most effective pre-filter costs nothing and is not a filter at all: time. Fill a bucket, walk away for half an hour, and most suspended sediment is on the bottom. Everything below is refinement on that.

4.1 Pre-filtering: three tiers

4.1.1 Good — about $0

Let it settle, then decant. A collapsible bucket filled and left standing for 30 minutes drops the bulk of its suspended load. Pour the clear top two-thirds into the dirty bag and tip the last third — and the silt with it — back onto the ground away from the source. This alone does more for cartridge life than any product.

A bandana or an old cotton t-shirt rubber-banded over the bag mouth catches leaves, insects and grit as you pour. Rinse and re-use. ⭐ For a build already at its payload limit, this tier is genuinely defensible — it weighs nothing, costs nothing, and addresses most of the problem.

4.1.2 Better — about $10–25 ⭐ recommended

Nylon paint strainer bags. Sold in packs for a few dollars, the 5-gallon size has an elastic rim that fits a standard bucket, and the mesh is fine enough to stop everything a membrane cares about while passing water freely. They are washable, they dry in minutes, and they are the right shape for the job by accident. ⭐ This is the sweet spot — the cost is trivial, the weight is grams, and it turns a bucket into a proper first stage.

Add a float intake. ⚠ Where you draw from matters as much as what you draw through. The bottom of a lake is silt; the surface carries film, pollen and scum. Draw from mid-depth. A short length of hose with a float — a scrap of pool noodle works — and the intake sits where the water is cleanest. This is standard practice in water treatment and it is almost never done in camp.

4.1.3 Best — about $40–80

An inline sediment cartridge. A 5-micron spun-polypropylene element in a small housing, plumbed ahead of the main filter. It is the same thing a house whole-home filter does, at camp scale. It turns the expensive membrane into something that only ever sees pre-clarified water, and the sediment element is a couple of dollars to replace.

⚠ This tier is only worth it if sources are routinely turbid. On clear Upper Peninsula streams it is equipment looking for a problem. Buy it when the paint strainer starts loading up fast, not before.

4.2 The camp water scheme

The sequence matters more than any single component, and most of it is discipline rather than kit.

1. Choose the source. 🔴 Flowing over still. Upstream of camps and roads, not downstream. Never anything with a bloom, scum, paint-streaking or a musty smell — and no filter on this page changes that.

2. Draw from mid-depth, into the dirty bucket. Do not stir the bottom; do not skim the surface.

3. Settle, 30 minutes, if the water is anything other than clear.

4. Pour through the pre-filter — the paint strainer or the bandana — into the dirty bag.

5. Hang and gravity-feed through the main filter into the clean container. ⚠ The dirty bag needs about four feet of head above the clean side. A carabiner and a length of webbing off the XTR3 rack, the trailer rail, or a branch. Work out the hanging arrangement at home, not at dusk in the rain.

6. Dose for storage if the water will sit more than a day. Filtration leaves no residual; a small chlorine dose does.

7. Dispense from a tap or spout. Never dip a cup into the clean container — that is how a clean container becomes a dirty one.

4.3 🔴 The two-bucket rule

Two buckets. One dirty, one clean. Colour-coded, labelled, and never swapped — not once, not “just this time.”

⭐ This is the whole hygiene system, and it is why filtering everything is the right call. The previous volume argued for a single water standard because two standards create a failure mode. The same logic applies one level down: the moment a dirty bucket gets used for clean water because it was closer, the filter upstream stops mattering.

Store them nested with something between them, or in different places entirely. On this rig the dirty bucket lives with the recovery gear and the clean one with the kitchen.

4.4 The freezing protocol

🔴 Carry this over from the previous volume, because it is the failure most likely to actually happen on a Michigan truck.

Once a filter has been used it is wet inside, and a below-freezing night cracks the fibres invisibly — it will still pass water and no longer filter. A used filter never spends a freezing night in the truck bed. It comes into the cab, or it is dried thoroughly before it is put away.

⚠ If in doubt, blow through the clean end. A sound membrane resists hard. One that passes air easily is finished.

4.5 What to buy

Table 1 — What to buy

Tier	Kit	Cost	Weight
Good	Collapsible bucket + bandana + patience	~$20	~1 lb
⭐ Better	+ paint strainer bags, float intake	~$30	~1.5 lb
Best	+ inline 5 µm sediment housing	~$80	~3 lb

Start at Better. It is thirty dollars and a pound and a half, it addresses the actual failure mode, and it makes the difference between a cartridge that reaches its rated life and one that clogs in a season.

References

• Hollow-fibre filter care — silt and fine sediment load the fibres and collapse flow rate; backflushing restores most of it; pre-filtering prevents most of it.
• Filter freezing — trapped water expands and cracks the fibres; damage is not visible and the filter continues to pass water. Standard Sawyer Squeeze, Sawyer Mini and Platypus GravityWorks are not freeze-tolerant; the MSR Guardian and Platypus QuickDraw are engineered to be.
• Nylon paint strainer bags, 5-gallon size — elastic rim sized to a standard bucket; washable.
• Water and Hygiene vols 1–3, this project — the payload case, the filtration analysis, and the shower.