Carrying, filtering and storing water in the field

Where this page stops, and who takes over

Read this first, because it frames everything below.

A water filter is not presented here as something that makes water drinkable. This page reports what manufacturers state about their own equipment — the pore size in microns, the flow rate, the cartridge life in litres — and nothing more. Whether a particular source may be drunk, treated or avoided is decided by the manufacturer’s instructions for the device you own and by the authorities responsible for the area you are in. Those two sources take precedence over anything written here, and where they say something different from what you expected, they are right and the expectation is wrong.

With that fixed, the rest is a procedure.

1. Plan the carry before the trip, not at the trailhead

Work out where along the route you can refill, and carry against the gaps between those points rather than against the size of the container you happen to own.

The reason is weight. Water is roughly a kilogram per litre, which makes it the heaviest single thing most people carry and the only one whose weight is chosen hour by hour. A capacity figure on a bladder tells you how much you can carry, never how much you should.

Note also that a full container is a load in its own right at camp. A gravity bag hung from a branch and a camp shower filled to its stated capacity both weigh at that same rate, and a branch that holds an empty bag proves nothing about a full one.

2. Choose the container by its mouth, not its litres

The specification that decides what else your water system can do is mouth diameter.

• The 63 mm wide mouth is the de facto standard that filters, gravity bags and insulated sleeves are built around.
• A 42 mm narrow mouth drinks more cleanly on the move and accepts far less.

The two families do not interchange. Adapters exist and leak more often than the bottle does. If you already own a filter, buy the bottle whose thread it fits rather than the other way round.

Material follows: copolyester lets you see the level, HDPE is lighter and slightly flexible, and single-wall stainless takes boiling water where the maker says so.

3. If you use a bladder, work out how it dries first

A hydration bladder is shopped on litres and thrown away over drying. Before anything else, look at the opening: a wide slide-top or a full-width screw cap can be turned back on itself and hung flat, and a narrow port cannot.

Then the three specifications hidden in the hose. Internal diameter sets how hard you draw. The bite valve may or may not have a shut-off, which is what stops a pack soaking itself in transit. And the quick-disconnect at the reservoir decides whether you can lift the bladder out to refill without threading the tube back through everything.

Makers state whether the reservoir may go on the top rack of a dishwasher, and that claim is worth finding: the alternative is a brush set and a drying frame.

4. Read the three figures a filter maker publishes

Once the container is settled, a filter is compared on published numbers and on nothing else:

• The stated micron rating. The pore size the maker states, commonly quoted to two decimal places on hollow-fibre cartridges — 0.1 or 0.2 µm are the usual figures. It describes what the element is built to hold back, as stated by the maker.
• The stated flow rate, in litres per minute. Measured on a clean cartridge, and it falls as the element loads. A starting point for comparison rather than a promise.
• The cartridge life, quoted in litres. This is the figure that decides running cost, and it varies by more than an order of magnitude across the shelf. Divide the price by that number rather than comparing headline prices.

None of the three is a statement about a particular stream. They are statements about a product, published by the company that made it.

5. Match the format to how you actually drink

Format changes the daily experience more than the element does.

• Squeeze bottles and pouches: fastest to use for one person, drunk from directly.
• In-line units: sit on a hydration hose, so there is no separate step at all.
• Gravity bags: fill once, hang, and let a group’s worth run through while you do something else.
• Pump filters: heavier and slower, and the only format that works from genuinely shallow water.

Check whether the housing takes a standard bottle thread, and whether the maker supplies a backflush syringe or coupling, because a cartridge that can be cleaned in the field lasts a trip longer.

6. Collecting: the step before the filter

Whatever the device, the collection step is where most of the practical difficulty lives. Take water from moving water rather than standing where you have the choice, take it from above the surface layer rather than by scooping the bottom, and use a wide-mouthed container or a dedicated dirty bag rather than fighting a narrow neck in a current.

Keep the clean and dirty parts of the system physically apart: separate containers, marked, packed in different places. Every filter maker’s instructions say some version of this.

7. Follow the manufacturer’s sequence, in order

Every device has a published routine, and the four steps are usually these:

1. Prime or wet the element as the instructions describe before first use.
2. Filter at the rate the device allows, without forcing it. Forcing a loaded element is how housings and seals fail.
3. Backflush at the interval the maker gives, using the supplied syringe or coupling, to restore flow.
4. Dry and store exactly as stated. Storage and freezing are what end most cartridges early, well before the rated litres.

If the instructions and this page ever disagree, the instructions win.

8. Storing water at camp

At a pitch, collect once and store rather than walking to the source repeatedly; a gravity bag or a large container does this well. Keep containers off the ground and shaded, keep the lids on, and keep the clean container clean by never letting a dirty one touch its opening.

Where a camp shower or a washing arrangement is involved, greywater and washing rules are set by the site and by local authorities rather than by the equipment, and they vary widely.

9. When you get home

Empty everything. Dry the bladder open and hung flat, dry the bottle with the lid off, and treat the filter exactly as its instructions require — the storage step is the one that decides whether the cartridge is still working next season.

Write the model number of the filter and its housing on a card and keep it with the kit. Cartridges are listed by the housings they fit, visual similarity between brands means nothing at a seal, and the moment you need a replacement is not the moment to start looking for the number.