Gravity vs Pump Water Filters: Which Suits British Water?

If you ever need to find your own water in Britain, on a long walk or because the taps have stopped, carrying a way to treat it beats carrying the water itself. A litre weighs a kilogram, so three days' worth on your back is nine kilos before you've packed anything else.

That leaves the question that fills forums, comment sections and our own inbox: gravity filter or pump filter? There isn't a single right answer, but there is a right answer for you, and it depends more on where your water will come from and who you're filtering for than on any spec sheet.

The Real Question Isn't "Which Is Lighter?"

Most comparison articles are written for backpackers. That's fine as far as it goes, but a walker on Scafell Pike is solving a different problem to someone who's had to leave a flooded town with their family.

The backpacker cares about grams and flow rate. They'll be back at the car park in four days, the water is coming from a clean upland stream, and if the filter clogs they'll buy another one.

For a household kit the questions are different. Will the filter still work after two years in a cupboard? What if the only water nearby is a field ditch churned up by livestock? What if there's no shop open to sell you a replacement cartridge? What if you're filtering for the whole family, children included? Those needs push you towards different kit.

If you haven't yet thought about when and why you might need to leave home, our piece on when you might have to leave home in a hurry is worth reading alongside this one. Your water plan should follow your plan for getting about, not the other way round.

The Contenders at a Glance

Pump filters work exactly as they sound. A hose goes into the water, you work a lever or piston, and clean water comes out of the other end into your bottle. Think Katadyn Hiker, Katadyn Pocket, MSR Guardian or LifeSaver Wayfarer. Worth knowing before you shop: the last two are purifiers rather than plain filters, so they remove viruses as well as bacteria and protozoa. Most pump filters don't, and that one capability accounts for most of the price gap.

Gravity filters are simpler and cleverer at the same time. You fill a dirty bag, hang it from a branch, and gravity does the work while you put the kettle on or pitch a tarp. Think Platypus GravityWorks, the Sawyer One Gallon system or the LifeStraw Peak Series 8L.

Sitting between the two are squeeze filters, which is where most British kits actually end up. The Sawyer Mini and Sawyer Micro Squeeze are made to be squeezed by hand, and hung from a branch below a full pouch they'll run as a slow gravity system too.

Here's the honest side-by-side:

That table doesn't crown a winner. What it shows is that the two designs struggle in different places, which is the most useful thing to understand before you spend your money.

Gravity Filters: Let Gravity Do the Work

With a gravity filter you do about ninety seconds of work, then the system runs itself while you get on with something else.

Where Gravity Wins

It saves effort. Standing over a pump for fifteen minutes to fill four litres for a family is fifteen minutes of hard work you didn't need to do, usually when you're already tired. Hang a gravity bag from a branch and it fills the same four litres while you're pitching a tarp.

It scales. One four-litre system can serve a family or a small group. Fill the dirty bag once in the evening, run it into a collapsible container, and there's water for cooking, drinking and washing up by the time the stove's lit.

It's simple. Two bags, a hose and a cartridge. There's no lever to snap and no piston to seize, so fewer things can go wrong after two years sitting untouched in a loft.

It becomes a tap. If you're staying put for a few days, hang it from a beam with a container underneath and you've got running water in a way a pump never gives you.

Where Gravity Falls Down

It needs somewhere to hang. That sounds trivial until you're in an open field, on a beach or on moorland with nothing above waist height for half a mile. You can improvise with a walking pole, a fence post, a gate or a rucksack propped against a wall. The dirty bag needs a metre or so of height above the clean one to flow properly.

Filling can be awkward. How awkward depends on the bag. A narrow-mouth pouch needs water deep enough to submerge it, often fifteen to twenty centimetres, and plenty of British sources don't offer that: a field runnel, a trickle over rocks, a shallow ditch, the last few centimetres of a stream in August. A wide-mouth bag, like the one on most proper gravity systems, fills far more easily from a shallow source. Either way, a scoop helps (more on that below).

Cold is its enemy. Gravity systems have long hoses and folded bag seams that hold water. If a wet hollow fibre cartridge freezes, the ice can split the fibres inside it. It will still flow and still look fine, but you can no longer trust it to filter, and there's no way to tell by looking.

It's slow to the first drink. If you just want a mouthful now, a gravity setup is a five-minute job. A pump gives you a drink in twenty seconds.

Tip: keep two metres of paracord with your gravity system. A short length with a loop tied in one end turns almost any tree, fence, gate or vehicle into a hanging point in seconds. It weighs next to nothing and removes the design's biggest limitation.

Pump Filters: The Versatile Workhorse

A pump filter answers the question "what if the water isn't convenient?" In real life, it very rarely is.

Where Pumps Win

Shallow water is no obstacle. The intake hose is the key feature. It usually has a small float and a pre-filter screen, and it will draw from a couple of inches of water in a rut, a rock pool or a cattle trough. You can lower it into a well or over a steep bank. That flexibility is worth a lot when you don't know what water you'll find.

You control the process. You feel the resistance build as the element clogs, so you can slow down, pre-filter the water and try again. A gravity system just slows quietly to a drip.

Water on the move. Stop at a stream, pump a litre straight into your bottle and keep walking. For one person covering distance, that rhythm is quicker in practice than setting up a gravity bag, even though the flow rates look similar on paper.

The good ones are serviceable. The Katadyn Pocket has a ceramic element you can scrub clean with the supplied pad, restoring the flow again and again, and the pump body can be rebuilt with a spares kit. Katadyn rates the element at up to 50,000 litres, depending on water quality, and gives the filter a 20-year warranty. That's a number for years of household use, not for a weekend.

Where Pumps Fall Down

They take effort. Pumping four litres through a part-clogged element is a proper workout. Do it with cold hands, in the rain, crouched on a slippery bank, and you'll see why gravity systems sell so well.

Moving parts can break. Handles snap, O-rings perish, and seals dry out after years in storage. None of it is common, but a pump that has failed mechanically is dead weight unless you carry the spares.

They're bulkier. A good pump with its hoses and pouch is a fist-sized lump of rigid kit, while a gravity system packs flat. If you're packing a slim 25 to 30 litre day pack, that matters.

It's one bottle at a time. Filling five bottles by hand at a rest stop is a chore.

The Shallow Water Problem

A pump's hose can draw from the shallowest puddle. A gravity filter needs somewhere to hang and a way to fill its bag.

This deserves its own section because it's the practical difference that catches most people out, and it's almost entirely missing from American gear reviews written around deep mountain lakes.

Think about the water within three miles of your front door. In lowland Britain you're likely looking at drainage ditches, field runoff, a canal, a slow silty river with steep muddy banks, a farm pond and a few seasonal streams that shrink to a trickle by midsummer. Not many of those will let you dunk a narrow-mouth pouch.

You have three ways round it:

• Carry a scoop. A collapsible water bowl, a cut-down bottle or a mess tin lets you ladle water into a bag from a puddle. It's slower and it's one more item, but it works.
• Dig a seep well. Scrape a hole about a metre back from a boggy seep or the edge of a shallow stream, let it fill, let the silt settle, and scoop from the top. It's a proper bushcraft skill, worth practising before you need it, and it turns unusable ground water into something you can work with.
• Use a pump. Drop the hose in and you're done.

If your likely water sources are shallow, silty or hard to reach, a scoop or a pump earns its place. If you'll be near a decent river or a known reliable source, gravity is fine.

What the Hiking Reviews Miss

Three things get too little attention in mainstream gear reviews, and all three matter for kit you might rely on at home.

1. A Filter Is Not a Purifier

A standard 0.1 micron filter stops bacteria and protozoa. Removing viruses takes a purifier (around 0.02 micron) or a chemical step.

This is the most important technical point in this article.

Most popular hollow fibre filters, including the Sawyer range, have a pore size of 0.1 microns. That's small enough to block:

• Protozoa such as Cryptosporidium and Giardia, typically 1 to 15 microns.
• Bacteria such as E. coli, Campylobacter and Salmonella, typically 0.2 to 5 microns.

It doesn't block viruses. Norovirus, rotavirus, hepatitis A and enteroviruses measure roughly 0.02 to 0.1 microns, small enough to pass through a 0.1 micron filter. To remove viruses physically you need a purifier with pores of around 0.02 microns, such as the MSR Guardian or a LifeSaver system, or a chemical or UV step to kill them.

Does that matter in Britain? For water from a clean upland stream in normal times, the risk from viruses is low and a 0.1 micron filter is sensible kit. That's why walkers use them and why we're happy to stock the Sawyer range of water filters. They're clever bits of engineering, they weigh almost nothing, and they're rated for large volumes.

It matters more when things have gone wrong: after a flood, when drains have overflowed into streams, or when sewage treatment has stopped. Human waste is the main route for viruses into water, and in those conditions a 0.1 micron filter handles the bacteria and protozoa but not the viruses.

The practical answer for most people is a good 0.1 micron filter for weight and speed, plus a chemical backup. A pack of water purification tablets weighs about as much as a chocolate bar, costs a few pounds and covers the virus gap. Filter first to remove the sediment and protozoa (Cryptosporidium in particular is hard for tablets to kill), then treat the water to deal with any viruses. That layered approach is cheaper and more robust than relying on any one device.

2. Longevity: Hollow Fibre vs Ceramic

Hollow fibre cartridges are bundles of tiny straws with microscopic pores. They're light, they flow fast, and their rated lifespans can be very long. But they clog with fine sediment, can only be cleaned by backflushing, and can be ruined by freezing once wet.

Ceramic elements are the opposite: heavier, slower and dearer, but you can scrub the outer surface with an abrasive pad to remove the clogged layer and restore the flow, many times over. Ceramic also copes better with silty water. The trade-offs are that it's brittle, so a hard drop can crack it, and every scrub wears a little away. That's why the Katadyn Pocket comes with a gauge: once the gauge slips over the worn element, it's time for a new one.

For kit you'll store for years and hope never to use, a buy-it-once ceramic pump has real appeal. For a filter you'll actually take wild camping, hollow fibre's low weight is hard to argue with.

3. Muddy Water

Think of it as the chocolate milk problem. Water that looks like chocolate milk is full of suspended clay and organic matter, and it will clog any microfilter, gravity or pump, in minutes rather than hours. Push a couple of litres of really muddy water through a fine hollow fibre cartridge and you may have reduced its flow for good.

The fix is a pre-filter, and it's the cheapest insurance in your water kit.

Tip: the shemagh strainer. Fold a shemagh into four layers, drape it over the mouth of a container and pour your dirty water through it. It catches leaf litter, grit, insects and a good share of the silt. Better still, let the water stand for an hour first so the heavy sediment settles, then pour the clearer water off the top through the cloth. Your filter will last far longer. A coffee filter, a clean sock or a folded bandana works the same way.

Filtering From a British Stream

Here's the part most guides skip, because most guides are written in Colorado.

Almost all British water runs through farmland. That stream in the valley has, somewhere upstream, passed a field of cattle, a slurry spreading operation, an arable field sprayed with pesticide, or a lane where road runoff drains straight into the ditch. Lowland England in particular is one large managed catchment.

That means three kinds of contaminant:

• Biological. Livestock carry Cryptosporidium, Giardia, E. coli O157 and Campylobacter. Any decent microfilter handles all of these. This is the easy part.
• Chemical. Nitrates from fertiliser, pesticide residues, hydrocarbons from road runoff. A microfilter does nothing about any of this, because pore size is irrelevant to a dissolved chemical. The practical answer outdoors is activated carbon, which reduces a broad range of pesticides and other organic chemicals, and most of the bad taste and smell too. It won't remove nitrates.
• Heavy metals. Old mining areas in Cornwall, Wales, the Pennines and parts of Scotland have left traces in some watercourses. Carbon and specialist media help; a standard microfilter doesn't.

So for British water it pays to think in stages: something to remove sediment, something for the biological risk, and activated carbon if chemicals are a concern. Some bottle filters build a carbon stage in. Whichever route you take, don't assume your microfilter is dealing with farm chemicals, because it isn't.

So Which One Should You Choose?

Choose a gravity filter if:

• You're filtering for a family or group. Two adults and two children need roughly eight to twelve litres a day for drinking and cooking alone, and pumping that by hand every day gets old fast.
• You'll mostly be staying in one place, so the filter's main job is supplying a camp or a house rather than water on the move.
• Your nearest water is deep enough to fill a bag from (a decent river, a lake, a reservoir, a full canal), or you'll carry a scoop.
• You want the simplest system with the fewest moving parts.
• You'll also use it wild camping, where hang-it-and-forget-it is a real pleasure at the end of a long day.

Choose a pump filter if:

• You're on your own or in a pair, moving through varied country rather than staying put.
• Your likely water is shallow or hard to reach (ditches, wells, steep-banked rivers, shrinking summer streams).
• You want a scrubbable element you can keep going rather than a cartridge you replace.
• You expect to use it in cold weather, where a hose full of standing water is a liability.
• You'd rather have a quick drink than a large unattended volume.

Or choose a squeeze filter if:

• Every gram counts. A squeeze filter with a couple of pouches gives you most of the capability at a fraction of the weight and bulk, and it can run as a basic gravity system by hanging the dirty pouch.
• You're new to this and want something that just works. A squeeze filter, a bottle filter or a personal straw is a sensible place to start, and our beginner's guide will help you fit it into the bigger picture.

Our Honest Verdict

If we had to send one person out of the door tomorrow with one water system, here's how we'd split it.

Our all-round pick: a squeeze filter backed by tablets, plus a scoop. It's light, affordable and simple to use, the tablets close the virus gap, and a collapsible bowl gets round the shallow water problem. For most people it's the most robust combination for the money, and it copes well with awkward British water.

For families and base camps: a gravity system. If you're filtering for several people or staying in one place, the effort it saves is huge. Add a carbon stage and a pre-filter cloth and you've got a proper water station.

To buy once and keep: a ceramic pump. Heavier, dearer and slower, but scrubbable, rebuildable and rated for tens of thousands of litres. If your plan is to stay at home through a long disruption, it'll go a very long time before it needs a new element.

The smart answer: carry two, and make them different. A light filter plus a strip of tablets weighs less than most people's spare torch. Water is the one place where we'd tell you not to count grams too hard.

Our full water filters and purification range covers gravity systems, squeeze filters, personal straws and tablets, and we only sell what's in stock. If you're not sure which suits you, ask us. We reply within 24 hours, every time, and we'd far rather point you at the right thirty-pound filter than sell you the wrong hundred-pound one.

Packing It Properly: Five Rules That Save Your Filter

Buying the right filter is half the job. Keeping it working is the other half.

Never let a wet hollow fibre filter freeze. This is the big one. Ice can split the fibres, and the filter will still flow but can't be trusted, with no way to tell by looking. In winter, keep it in your sleeping bag or an inside pocket. If you think it has frozen while wet, treat it as damaged and fall back on tablets or boiling.

Backflush it, then store it dry. A wet filter left in a rucksack for six months grows things. Backflush it clean, shake it out, let it air dry for a day or two, then bag it.

Bag it separately. Put the filter in a small dry sack so a leaking hose can't soak your spare socks and the clean end never touches anything dirty.

Pack it where you can reach it. A filter at the bottom of a 60 litre rucksack is a filter you won't use at the stream you passed twenty minutes ago. Top pocket or side pocket.

Try it before you need it. Take it wild camping. Find out now that the hose clamp is stiff, that your bag won't fill from the stream near you, or that the pump handle needs two hands. A pleasant Saturday is the time to learn your kit's quirks.

A Last Word

Nobody posts photos of their gravity bag. But a stomach bug from a farm ditch is the last thing you need when you're already cold, tired and a long way from home.

Pick the system that matches where your water will actually come from and how many people you're filtering for. Add a pre-filter cloth and a strip of tablets. Practise with it twice. That's the whole job, and it costs less than a decent pair of boots.

Get it sorted, then get back to the fun kit.