RapidPure Filters Review

[Stephanie Jordan]

Companion forum thread to:

RapidPure Filters Review

[Robert Langer]

Great article, thank you Roger!

One question regarding the expected filter life: In their tech data sheet, rapid pure claims 11,000 gallons of filter life (see http://www.rapidpure.net/Documents/RapidPure%20Tech%20Data%20Sheet.pdf). Your test shows a significant slow down after just a few liters. So how realistic is rapid pures claim from your point of view? What is a realistic amount of filtered water from your point of view?

And one more thing: Is there a way to backflush the filter? The Sawyer Squeeze is definitely a pain for a long thru-hike but at least you can backflush it.

Thanks for the answers in advance!

[Tom Andrews]

Hi Roger,

So, even with all this fine detail, I am a bit confused about what or if you would recommend this system for the light-weight or ultralight-weight backpacker. Which of these systems would you recommend, what would be the total weight of such a system, and how long would it normally take to filter a quart of water? I have been using Aquamira drops or tablets and have been satisfied with the weight, but not always with the waiting time. My use of a Sawyer system failed due to too much filter blockage and my UV experience with batteries was dismal. So a really light weight filter system would be ideal. However, my old brain just can't grasp whether or not the system you describe would do it.

Thanks,

Tom

[David Wood]

Great article as always Roger!

I've been trying to figure out if these things can be trusted for years: http://www.drinksafe-systems.co.uk/

They make great claims but do not post lab reports. I've managed to obtain a rather poor set of copies of lab reports from them but I can't really verify them myself of course. Their site claims a fair bit of testing but nothing very verifiable: http://www.drinksafe-systems.co.uk/worldwide-testing.php

I'd love to know the tech they're using but would love even more to know if their kit is as good as it claims!

[Michael Matiasek]

Thanks for taking the time to review this exciting new product! Would it be possible to add some units to the axes of your graphs. It would make it easier to interpret your data. Thanks!

-Mike

[Ross Bleakney]

This is a nice article, but it would be nice if there was a more apples to apples chart comparison with these filters and the Sawyer filter. The Sawyer filter is pretty much the standard filter for a lot of backpackers. It clogs up pretty quickly, so my guess is that you would see similar degradation numbers, if not worse than the other filters.

My setup (which I know is common) involves a Sawyer bag, the filter, a (cut down) Tornado Tube, a Platypus, and a few assorted caps. I also carry a syringe for back flushing. This setup allows me to drip filter or use the sip-and-go method if I'm in a hurry. This is a fairly light setup, and fairly convenient. For example, if I'm passing a lot of streams, I don't carry water, nor do I spend as much time as I would with a pump, let alone a drip filter. But in camp, or while taking a snack break, I let it drip.

Compared to using one of these filters, I think the Sawyer's main advantage is the housing. You can achieve the same sort of thing with plastic tubing (turning any filter into a squeeze filter or a drip filter), but there are disadvantages to that. Not only does it add weight, but it means that the clean bottle (the platypus in my case) doesn't have to sit on the ground. This makes the hanging process a lot easier.

That being said, I would love to see a weight comparison of similar systems. For the RapidPure filter, this would mean adding the set of connecting adapter tubes of minimal weight and compare that to the weight of a chopped Tornado Tube. The weight of the bag is meaningless, as you can use any bag with the right adapter. Likewise, the weight of the syringe would be the same, although the RapidPure might need another bit of tubing for this.

From what I can tell, all of the RapidPure filters are heavier, but all of them filter faster. It looks like almost all of the extra weight is due to the housing, not the filter material itself. The Tornado Tube setup (no tubing and only 14 grams) might also save a little weight.

[Nico .]

Interesting review of new filter options. I've previously used this technology in an old first need purifier. As noted in the article, the first need was heavy, but otherwise worked very well with all sorts of iffy water in multiple countries. I've hung on to it after all these years in the event of future international jaunts.

The various bottles, bags, etc. offered are of no interest to me, but the potential to cobble together my own inline system with one of the new Rapid Pure filters is an interesting option. Especially if you're getting purifier-level performance at typical water filter weights. It might not replace my Sawyer Squeeze for most solo short trips but it might have a place in my quiver for group trips and/or travels through areas where viruses are more of a concern.

I'll be doing some more reading and looking into these offerings. Thanks for bringing them to our attention.

[Michael Sirofchuck]

I am using the lightest Sawyer filter at this time and have been very happy with it. I generally try to backwash clean it after every couple of sessions, depending on the water I am filtering. While the RapidPure seems to be pretty good, I'm not convinced that I'm saving weight or money by replacing my Sawyer at this time.

[Roger Caffin]

Hi Robert

LIFE – always the big question.
It is going to totally and entirely depend on how clean the water is to start with. There are NO definite answers.

There seems to be some very fine suspended algae in my dam water, so that is a tough test for any filter. With cleaner water, as from a clear mountain stream – you should get a 'long' life.

Backflush – not tested. You could try. For bacteria etc caught inside the filter backflushing will have no effect, but for algae caught on the surface it might blow it off. I must ask RP about that. Note that if all you are catching is bacteria, the life of the filter will be 'very' long.

Cheers

[Colin Krusor]

I share Robert's interest in the life (capacity) of the RapidPure filters. Once particles in the source water have become electrostatically associated with the filter media, those sites on the media are occupied. There are no longer positive charges at those sites reaching out to attract net-negatively charged bacteria and parasites in the stream of water passing through.

So, it seems to me that, unlike a physical filter like the Sawyer Squeeze, the RapidPure filter should start to allow pathogens to pass through at the end of its life, when all of the positively charged sites on the media are occupied. Many of the openings in the RapidPure filter media are larger than the pathogens, according to the above article. A Sawyer Squeeze that is undamaged will never allow bacteria or parasites to pass through, no matter how old it is. The RapidPure company would not volunteer this in their product literature, I assume, but is this in agreement with your understanding of the filter design, Roger?

If this is correct, users are at risk. It's not the volume of filtered water that determines filter life, but the absolute number of charged particles in the source water, which depends on water turbidity, pH, and other factors. A user has no way to know if the charged sites on the filter media are nearly used up.

Can particles entrained on the filter media be backflushed off with a concentrated salt solution?

[Roger Caffin]

Hi Tom

> if you would recommend this system for the light-weight or ultralight-weight backpacker.
Short answer: to each his own. OK, that does not help!

Yes, I think I could recommend this system if filtration is your thing. The little 2.5" Scout might be OK for a couple of nights IF you know the water will be clear. The larger ones seem to have a much better life. Certainly, the larger ones are fast!

Cheers

[Roger Caffin]

Hi David

> http://www.drinksafe-systems.co.uk/
Yeah, NOT a very helpful web site. Very spin-oriented, which never impresses me. Usually just makes me suspicious.

They make lots of claims, but a harsh legalistic judgement would have to be that they do not meet EPA requirements. The figures they quote are not good enough as far as I can see. I may be wrong of course: I can only go on what they put on the web site.

Cheers

[Roger Caffin]

Hi Michael

> add some units to the axes
OOPS!
The units are givin in the text – litres and minutes, but not on the graphs themselves. I will see if I can fix that.

Thanks

---

Edit: graphs changed to have units on them now.
Thanks Michael.
Cheers
Roger

[Ross Bleakney]

>> The little 2.5" Scout might be OK for a couple of nights IF you know the water will be clear. The larger ones seem to have a much better life. Certainly, the larger ones are fast!

OK, but if I read the article correctly, the little Scouts are better than a big Sawyer filter. Did I get that right? If so, you are saying that bringing a (standard) Sawyer filter is OK for a couple of nights, IF you know the water will be clear …

Did I miss something?

[Roger Caffin]

Hi Colin

> the RapidPure filter should start to allow pathogens to pass through at the end of
> its life, when all of the positively charged sites on the media are occupied.
Technically correct.

However, you need to keep two things in mind when considering this. First is RP's actual claim:
' Rapid Pure filters have a rated life of roughly 3750 gallons per inch of media. '
That's a lot of water: would you ever pass that much through a filter in your walking life? Let's say you filter 2 gallons per trip, for 10 trips per year, for 10 years: that's 200 gallons.

Second is the far more realistic question of whether you will ever get that much water through the filter before the surface is blocked with algae and other muck. I rather think that surface blockage is going to happen YEARS before the filter even reachs 50% capacity for bugs.

> Can particles entrained on the filter media be backflushed off with a concentrated salt solution?
I do not think this is even remotely possible.

Cheers

[Roger Caffin]

Hi Ross

Yes, I think you are missing the whole point. The RP filters give about ten times more flow than the Sawyer filters at the same pressure.

Cheers

[Ross Bleakney]

Thanks Roger, that is what I thought. That is why, with all due respect, suggesting that it is "OK for a couple of nights IF you know the water will be clear" is way too pessimistic. Plenty of people use the Sawyer, and it is ten times better than a Sawyer. TEN TIMES! The only issues are weight, longevity, and maybe the adapters (e. g. the convenience of a Tornado Tube). Other than those issues, the smallest RapidPure is much better than what most of the people I know use, and the bigger ones are even better than that.

[Colin Krusor]

I disagree with your reasoning, Roger. I've spent the last four years as a graduate student doing waterborne pathogen lab and field research and I thought carefully about my question before I posted it. It's clear that a person won't filter 11,000 gallons of water. But "bugs" aren't the only things that compete for charged sites on the filter. Tannins have net negative charges within the usual pH range, as do many species that fall within the "dissolved organic carbon" category. These organic anions will not foul the filter but will occupy charged sites. A couple of gallons of tea-colored tannin-rich water from a forest stream will contain an unfathomable number of organic anions eager to mask any positive charge on the filter media.

I'm not trying to push you for information you don't have, and I'm not suggesting that a person will ever pass thousands of gallons of water through their filter. I'm just observing that this filter design appears to have a problem: its remaining life cannot be estimated by the user because of variations in source waters, and when the filter approaches the end of its life, it starts letting pathogens through.

[Roger Caffin]

Hi Colin

> its remaining life cannot be estimated by the user because of variations in source waters,
No argument.

So maybe, when the filter element looks a bit discoloured and it is several years old, you replace it? Nothing lasts forever. Reckon that might work?

Cheers

[Colin Krusor]

I'm not fond of relying on my reckoning for determining whether the filter will remove pathogens. Organic anion concentrations vary over many orders of magnitude in environmental surface waters. If published RapidPure capacity testing results come from testing against low-ion source water, the filter capacity for tea-colored forest stream water might be 20 gallons. We don't know how to guess how much water volume, or filter discoloration, indicates that it's time to replace it.

The problem remains: if you guess wrong, your filter's function appears the same, but free pathogens now flow right through into your drinking water. That's unique to this filter design.

[Andy Jarman]

Thanks Roger. I've been hovering between my Steripen (hate batteries) and Sawyer squeeze mini (those pigs and goats do not just bath in the puddles I drink from). This looks like an answer, EXCEPT, how do you know when it has stopped working, or will stop working. Both from the point of view of clogging and from the viral neutralizing point of view. Can anyone help with this important factor?

I suppose I could do as I do now and just take along some tablets for suspect looking water, but I'm not sure I'll ever trust a viral filter that doesn't have a use-by date on it.

[Roger Caffin]

Hi Andy and Colin

Good questions.
I will try to ask RapidPure for comment.

Cheers

[Walt Bizzare]

I'm a big fan of bleach. Clean your water bottles, bladders and maybe filters when you complete a trip. I'm wondering if bleaching the filter would restore it's function?

[Ken Thompson]

Any problem with freezing?

[sean neves]

I gave up on filters ten years ago but continue to buy the latest and greatest just to proof the tech. I am a bit of a tinkerer and am constantly working on solutions. The problems with various solutions are: in-bottle filter means you're tied to a proprietary bottle. I don't like proprietary stuff. In-line, in-use (water filter on bladder, on pack), is too hard to suck. Gravity always clogs because the filter sees all debris. They should really start putting the line feeds and filters on bag systems to the side of the bag, letting debris settle before the filter, but that creates an available head/pressure issue. Once primed, the "micro-tube" tech is full of water and twice as heavy. Back-flushing is iffy at best. All filters fail, so you sort of have to bring chemical backup. That's my theory on all mechanical and electronic systems. Applies to UV tech too. This tech addresses a few of those issues and I will test it for myself.

I have been using a Steripen/Uv with chemical backup for four years and it has proven pretty darn reliable and robust. I hate the wide-mouth requirement and the battery situation can be tough. I've found that you need to buy name-brand lithium and carry spares. However, I really wish Steripen would start utilizing the rechargeable 18650 format, which has proven reliable and robust in the multi-amp flashlight weenie world (read: CP Forum) where I sometimes dabble. I have already shifted all of my electronics to 18650 anyway and it would be nice to pop the cell out of my headlamp in the daytime to purify my water.

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