The answer — one pick, priced
Get the
Platypus GravityWorks 4L
$15 under your budget
Filters 4 litres hands-free in about 2.5 minutes while camp goes up — the group standard for 3-6 people across our 9 sources.
Fit ledger — need → measured evidence
■ The catch — co-equal billing, always
The replacement cartridge costs about $79. At 1,500 L that is roughly $0.05 per litre — three times a LifeStraw Peak membrane, and infinitely more than the Sawyer, which has none. It also needs a hang point and water deep enough to scoop the 4 L dirty bag, so shallow silty creeks are a bad match.
Dealbreaker? Sawyer SP129 ($46) each if the group splits up at the source ↓
■ Every product has a catch. Verdicts that hide it are how bad buys happen.
Don't buy this if…
- you need to filter water at home or for municipal tap waterUnder-sink water filter verdict →
- you need a large-group basecamp system filtering 10+ liters at a time
- you are traveling internationally and need virus removal from urban water
Wrong product for you is still a bad buy. These are the cases where we'd send you somewhere else.
Runners-up — if your needs differ
Adjacent verdicts — other needs, same method
Different budget, different household, different job — each of these is already researched, priced and verified. Take the one that matches your need.
Traps — this verdict avoids
Why the Platypus GravityWorks 4L is right for you
It avoids every trap below — and for family of 4, under $150, it is the pick because it delivers:
A filter is not a purifier
A 0.1-0.2 micron hollow-fibre filter removes 99.9999% of bacteria and 99.9% of protozoa — and zero viruses. North American backcountry is a filter problem; international travel, urban water and any source with human contamination upstream is a purifier problem.
One freeze kills it, invisibly
Water trapped in a used filter's fibres expands and cracks them with no visible sign. Cascade Designs states there is no way to confirm a thawed filter is still safe — it has to be replaced. Sleep with it in your bag below freezing; only the QuickDraw has a field integrity test.
The cartridge is the real price
Replacement membranes run $26-29 on the squeeze filters, ~$79 on the GravityWorks and $239.95 on the MSR Guardian, and the Grayl needs a $30 cartridge every 250 L. Only the Sawyer Squeeze has no cartridge to re-buy at all.
Provenance — 9 sources, dated
Winners are picked from the full research dossier at knowledgelib.io. Prices, stock and listings are re-verified monthly.