RapidPure Filters Review

[Sam Farrington]

Hi Roger,
As I am not science trained, it would be very helpful if you could indicate which of the RapidPure filters is the closest to the Sawyer Mini in terms of capacity, flow rate, and no greater size or weight. Or to put it another way, would be the most suitable to substitute for a Sawyer Mini in a SUL pump filter I'm making. I tried out a prototype this summer, and it worked far better than anything used previously; however, I learned first hand about the limitations on the Mini, particularly the useful time between backflushings. Having a little pump as part of the unit is great for backflushing though. I'm putting this on the thread, as others might also be interested in your opinion.
Thanks,
Sam

[Roger Caffin]

Hi Sam

As far as flow rate is concerned – for equal heights, the RapidPure ones seem to be about 10 times faster. This hard fact seems to be giving a lot of people much anguish, with all sorts of explanations of why it won't work.

Which unit to try – good Q, depends on the trip. But I would certainly be looking at either the long Scout or the short Explorer for trips under a week.

I would also be looking very seriosuly at trying to reduce the weight of the housings. They are all a bit over-engineered imho. But they would withstand most Boy Scouts or tourists.

I am currently still using my UV Opti, but I am keeping my options open.

Cheers

[Sam Farrington]

Thanks, Roger, for your response. Will proceed accordingly.

[Colin Krusor]

"This hard fact seems to be giving a lot of people much anguish, with all sorts of explanations of why it won't work."

Roger, to be fair, I don't think the concerns raised so far deserve this ridicule. I raised only one issue, based on good science, and it was validated by the manufacturer of the RapidPure filters. I brought to the attention of BPL readers a legitimate problem that the company confirmed.

Your article was excellent, and I greatly appreciate the work you did. Please don't take concerns about the RapidPure series of filters personally.

[Roger Caffin]

Hi Colin

> I don't think the concerns raised so far deserve this ridicule.
I also received some email which was a bit more 'pointed' in attacking RapidPure.

Cheers

[Colin Krusor]

Sorry to hear that, Roger. I've mentioned already my gratitude to you for putting the work into this article, and I give you credit for introducing a lot of readers (like me) to these filters and opening a discussion about them. I'm disappointed that someone was antagonistic about it.

[Roger Caffin]

Hi Colin

Comes with the territory. Doesn't worry me one hoot. Thick-skinned Aussie!

But yes, these filters do alter the scene, don't they? Whether they will work out in the long run – that we will have to wait and see.

Cheers

[Sam Farrington]

Roger,
A few more questions I guess.
You mention the long Scout "for trips under a week."
Since these filters do not appear to be renewable by backflushing, I'm wondering if you are suggesting that the useful life of the filter is only a week. Could you clarify a bit.

Since none of these filters appear to be designed for in-line use, they also appear to need the housings to enable that use. The longer Scout, with a 3.5" filter and housing, is 3.1 oz per the website. The shorter 2.5" one is stated to be 2.7 oz. Those are rather high, considering that water in the filter will add weight, and water in the housing will add even more.

I'm comparing the above with the Sawyer Mini, at 1.8 oz on my scale after drying out for a couple weeks. So it will require backflushing before its next use, but I found it required almost no effort to pump water through it using the Heinz Easy Pump suggested by David Thomas. So I went from ~70 difficult pumps with a Sweetwater Walk-About to ~30 effortless ones to pump a liter of water. And that was sucking the water up from the source through the Mini. Pumping from the pump through the Mini required far less pumps, but there were a bunch of reasons to suck, such as keeping the pump antiseptic and ease of use.

So even though these filters may require much less pressure, the amount needed to pump the Mini is already slight, the added weight of the RapidPure would probably be around a couple ounces at least, and there is the concern first raised above about useful life. Any thoughts you may have about any of this would be welcome. I appreciate your bringing this technology to everyone's attention, but have doubts about applications.

I certainly agree with your initial comments about pump filters to date. The irony is that my first Filter, a Pur product named "Pioneer," was around 8 oz, and had thin filtration discs about 4" in diameter that could quickly be swapped out. So another filter did not have to be carried as an emergency back-up, just a few extra discs. If the new technology were applied to the manufacture of those discs we would be in fat city. You are right about things improving, but they do not seem to improve smoothly, but rather by fits and starts.

[Roger Caffin]

Hi Sam

> that the useful life of the filter is only a week. Could you clarify a bit.
No, I am not suggesting that at all. What I am trying to do is to allow for the odd bit of slightly algae-loaded water. It complicates things.

If all you ever filter is clear water, then a Scout could last a long time imho – quite possibly many weeks or even longer. But can you be sure you will never find some algae? My thinking is that even if you do find a little bit of algae each night, a long Scout should survive a week-long trip. The filtration rate could well be a bit slower by the end of the week of course. pre-filtering the big lump out first would help.

> Since none of these filters appear to be designed for in-line use, they also appear
> to need the housings to enable that use.
Yes indeed – but so does ANY other filter element. There are NO filter elements which operate without a housing of some sort. The Sawyer has the filter element epoxied inside the housing, so that you have to buy a whole new housing and filter. Other filters allow you to replace just the filter element or cartridge.

What we have at present is V1 from RapidPure. I think the filter element is fine, with clean water, but the housing is a bit heavy. Can they make V2 lighter? I am sure they can, but is the UL market big enough for them to bother? I don't know.

Cheers

[James Marco]

> Since none of these filters appear to be designed for in-line use, they also appear
> to need the housings to enable that use.
Well, you don't need a housing, as is commonly understood. They have the Trail Blazer which is designed for attachment to your own housing be it a gallon jug, 5 gallon pail (as shown), or rigged to some other container (perhaps a Platy bottle.) They are a DIY'ers dream with just a filter and threaded component with tube spout at the one end for attachment. You could likely rig this to a small 1 qt milk bottle for smaller quantities for about an ounce or two. The milk bottles are fairly rugged and collapse fairly well in your pack. A larger dirty wter bottle can be used, of course. Or rig a stiffener on a dry bag and attach that inside, except when filling for about 3oz extra.

[Paul McLaughlin]

Roger – After reading the article and all this here is my impression:

1)The RapidPure filters work much faster than the sawyers – at least at first.
2)The RapidPures are NOT backflushable, so when they clog, they are done.
3)The RapidPures are slightly heavier than the sawyers (although they come in more sizes so this is not that simple).
4)You can carry just an additional filter element for a RapidPure as a backup.

Let me know if any of that does not accord with your findings.

Now based on that it seems to me that if you are dealing with water that is generally pretty clear – as in alpine lakes and streams (other than glacial silt situations), then the RapidPure filters could be very nice if speed is important to you. Overall life of the filter my be shorter without any backflushing capability, or maybe not given the larger pore size.
But if you tend to encounter dirtier water, then the likelihood of the RapidPure clogging goes way up and having to carry backup elements starts to make it look like the wrong choice for that situation. A backflushable filter seems like a safer bet there.

So nice for some uses, not as good for some others. Personally the speed doesn't mean much to me since I use a gravity setup and I'm in no hurry. So the lightest weight filter and simplest connections are most important to me. My guess is that if the folks at RapidPure are listening in they can drop the weight on their housings and become even more competitive. Hopefully just about the time my Sawyer is done for!

[Roger Caffin]

Hi Paul

A fair summary, all around.

I am not sure that there are ANY good soolutions for dirty water. Even back-flushing has its limits imho.

Cheers

[Jim Colten]

I know a few people who use these for pre-filtering solids:
0.5 micron – http://www.dudadiesel.com/choose_item.php?id=PTFEP3S
inexpensive and not heavy if you remove the stiff steel ring.

The vendor is candid that these are not absolute filters but they have a good record in the field when used in conjunction with your favorite filter or treatment method.

[Paul McLaughlin]

Jim, you bring up what I should have mentioned as well, that some sort of pre-filter for gunk/large solids is a must for dirty water or even just likely mild algae situations, regardless of the filter you like it will extend the life and/or reduce the need for backflushing. Coffee filters seem to be often used; some filters come with pre-filters of various types.

[Sam Farrington]

Thank you Roger and Paul for the clarifications in your recent posts. They were very helpful.
A major reason I use a pump is because I like to be able to take water from seeps and shallow sources in order to have more choices about where to camp.
Unfortunately, even with a good prefilter, this also means that the filter gets exposed to more gunk. The worst I've seen is the extremely fine silt in water holes on the Divide in CO. And yes, there is the algae also, which can be very fine.

I'm going to play with a Mini and different prefilters for a while longer, but if that doesn't work out well, will use a Scout and carry an extra filter cartridge. Thanks, Roger, for presenting a new alternative in your article.

[Roger Caffin]

Yeah, well, sometimes the water just is not 'suitable'. Then you need a two-stage approach: the first is to get the 'gunk' out of the water, because it is going to be 'big'; the second is to deal with bugs. They are smaller.

It just is not possible to get good results with a super-fine filter, which is what we need for the bugs, when the water is full of gunk. But this applies to EVERY water trewatment method, without exception.

Cheers

[Roger Caffin]

Hi all

Well, it seems RapidPure have been sufficiently impressed by the level of interest and technical discussion here that they are preparing a technical update with scanning electron microscope pictures of the filter medium, to show you just how it works. A little more than an 'REI Press release'.

What the update will emphasise is that the filter works in depth, so that surface clogging and 'filling up' does not mean bugs will get through. The pictures will show how this works.

It will take a few days for this to get through the system. I just thought it might be worth while giving you all a heads-up on it.

Cheers

[Eric Brewer]

After Roger's article first appeared, I ordered several different versions of the RapidPure to test. Picked a larger one (since I would be filtering for four people) to take on a 4-day trip to Vermont. Put it inline with a Platypus GravityWorks bag. To be blunt, it was a massive bust – 3 liters over each 8 or 9 hour night! We ended up boiling water and using my son's Sawyer Mini.

Got home yesterday and did what I should have in the first place. Absolutely stupid of me to not have tested more before leaving home. Of the 3 different versions I had purchased, I had picked the one faulty unit to take with us. The others worked wonderfully – as Roger said, at least one order of magnitude better than the Sawyer Mini.

So, take away point is to (duh!) do a reality check with your RapidPure filter before you go!

– Eric

[Ross Bleakney]

@Eric — Thanks for the heads up. That isn't a good sign, but it doesn't mean the technology is flawed (only that the manufacturing process is). That has happened to a bunch on companies, unfortunately.

I usually run a fair amount of tap water through my unit as soon as I get it anyway. I figure there might be spare bits of plastic in the housing that you might as well wash out (just as I always wash new clothes before I put them on). It would have been annoying either way, but not as annoying as what you endured.

Smart of you to have a spare filter. For bigger group trips, we always take a spare (for that reason).

[Ross Bleakney]

Getting back to the housing issue …

I find the housings for inline filters to be rather primitive. Several years ago, before Sawyer made an inline filter, I had a "squeeze" filter system, although I didn't call it that. I simply attached a few tubes, lifted the platypus and sucked through it. Sawyer deserves credit for connecting the filter housing directly to the water container (assuming they came up with the idea).

But they completely ignored the market for drip filters. As a result, people (like me) are left either chopping up a kid's toy (i. e. Tornado Tube) – which may not be food grade plastic – or they glue two caps together. Meanwhile, we are left fussing around with bags or coffee filters to do pre-filtering, a process which is hardly convenient.

It seems to me the filters should come with the following:

1) The same connections as a standard Sawyer filter. This allows you to screw on a "dirty" bag to one end, and a cap on the other. The cap can be a "popup" cap, which allow for easier "squeeze" drinking.

2) A separate Tornado Tube type adapter, which you can screw on, so that the filter can hold the weight of another water container.

3) A simple screw on pre-filter. This should be lightweight and contain a simple screen, which would mean it would be extremely simple to clean. It would have a male and female connector, so that screwing on a "dirty" bag works the same way.

4) Add little holes in the upper sections of water bottles, so that you can hang them upside down when you make a drip filter system. Since Sawyer sells "dirty bags", it would make a lot of sense for them to do this.

5) Sell water bags with ziplock openings (and the same holes as above). I think Platypus does this.

The last two are far less important to me than the first three. Making the holes is trivial, and ziplock openings are never going to be as secure as a solid bag. But the first three suggestions would make using these types of filters a lot easier.

[Kris Hampel]

I know this will go against the Ultralight grain since I'm talking about carrying another bit of gear, adding a second process (or more), adding further possible points of potential failure and/or operator error; but, since everyone seems to be whinging about the 'unknowability' of the filter state based on the 'unknowability' of the anion content in the water I ask:

What (if any) tests/equipment exist to quantify this prior to filtering?

I know zero about this stuff, so over to you ladies and gents with the big brains. But before that happens, I'm going to elaborate on my imagined device and the grandly over simplified principles and mildly plausible mechanisms on which it might operate.

This device would be some sort of small electrical device (thinking hacked Steripen looking gizmo) that could be dipped into a water sample to determine the anion or cation content using a charged electrode. Easy. Based on some relative measure(s) such as known sample volume, known surface area of the testing electrode/probe, known electrical properties of the testing electrode/probe, degree of eccentricity in the orbit of Saturn correlated against a liner regression of the estimates of 200 expert predictions on the outcome of the next sporting grand final (any sport should suffice according to my calculations), this little device then tells you how many itty bitty little negative charges are charging around in your water sample (expressed as a percentage, ratio, an absolute value in Roman Numerals, or as graph with axes marked in Cryllic numerals and labelled using Egyptian hieroglyphs – this is to ensure we are servicing the entire international market plus one idiot). All of this is is also easy, if (and only if) someone other than me does this part.

Once this mildly portable, mildly ultra lightweight device is found/built/grown+housebroken, you use it to forecast the suitability of the water for filtering. You could also log your filters anion exposure and estimate when you need to junk the filter. From this you would make your own assessment of filter life based on your own habits and decide on the suitability of the water source for filtering based on your own unique combination of cheapness, time to hand, prevailing weather conditions, how awkward your water source is to get at, remaining trip duration and how thirsty/desperate/nearly-dead-from-dehydration you are.

Anyway, like all visionaries, I consider my part in this enterprise to be fully realised. I will leave it to others to simply thrash out the minor details, such as 'how'…

[Eric Brewer]

RapidPure has asked for my incredibly slow filter for a "forensic teardown" so they ARE interested in perfecting their product. Shipping it off this afternoon.

– Eric

[Roger Caffin]

> This device would be some sort of small electrical device (thinking hacked Steripen
> looking gizmo) that could be dipped into a water sample to determine the anion or
> cation content using a charged electrode.
I think you are talking about a conductivity meter. Known device.
But it cannot detect or measure viruses, bacteria or protozoa in water. Pity.

Cheers

[Kris Hampel]

Similar I suppose. It doesn't need to measure the actual viruses or bacteria, as you don't necessarily care if the filters positively charged 'slots' are occupied with viruses or tannins or something else, you just need an indication of how much of the filter elements 'useful life' will be consumed by filtering that water. The device's sole purpose is to provide you an indication of the overall concentration of negatively charged particles in the water, from which you can make some sort of estimate as to how much of the positively charged surface of the filter will be occupied in the filtering process of a given amount of that water.

The obvious complexity is it probably depends not only on the concentration of anions overall in the water, it probably matters as to the size of those anions as well.

All of that aside, thanks very much for the article Roger, I appreciate the information you have provided.

[Roger Caffin]

Hi Kris

I think I see the problem.

> The device's sole purpose is to provide you an indication of the overall
> concentration of negatively charged particles in the water,

But NONE of the bugs are negatively charged in the sense you are thinking. They are NOT anions, they are all quite neutral. The surface of the bugs can be negatively charged, but the interior is positively charged to balance.

Anyhow, the bottom line is that they do NOT alter the conductivity of the water. If they did, trust me, we would have had that invention decades ago!!!

Cheers

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