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Reviews > Water Treatment > Solar > Puralytics SolarBag > Test Report by Rick Dreher

Test Series by: Rick Dreher

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Long-Term Report

Initial Report - May 20, 2015
Field Report - August 19, 2015
Long-Term Report - September ##, 2015


NAME: Rick Dreher
EMAIL: redbike64(at)hotmail(dot)com
AGE: 61
LOCATION: Northern California
HEIGHT: 6' 0" (1.83 m)
WEIGHT: 175 lb (79.40 kg)

I enjoy going high and light and frequently take shorter "fast- packing" trips. My longest trips are a week or so. I've lightened my pack load because I enjoy hiking more when toting less, I can go farther and over tougher terrain, and I have cranky ankles. I use trekking poles and generally hike solo or tandem. I've backpacked all over the U.S. West and now primarily hike California's Sierra Nevada. My favorite trips are alpine and include off-trail travel and sleeping in high places. When winter arrives, I head back for snowshoe outings in the white stuff.

Initial Report

Product Information & Specifications

Model: SolarBag water purification device
Manufacturer & Website: Puralytics
Weight (manufacturer): 4 oz/105 g
Weight, dry w/prefilter (measured): 3.6 oz/102 g
Capacity: 0.92 gal/3.5 L
Dimensions (empty): H: 15.7 in/40 cm W: 9.7 in/25 cm
Prefilter fabric: 40 wt Pellon
Prefilter effective pore size: 0.1 mm
Claimed treatment time: 2-6 hours
Claimed to remove/neutralize: Pathogens, chemicals, metals
Effective lifespan: As much as 500 cycles and seven years
MSRP: $100 US

Ships with

SolarBag, prefilter, marker dye, instructions.

Initial Impressions


SolarBag is a self-contained water purification and storage system. It is a flexible plastic bag that holds nearly a gallon (0.92 gal/3.5 L) and relies on sunlight to remove contaminants. SolarBag is claimed to remove/neutralize pathogens, chemicals and metals with no more effort from the user than filling it and leaving it in the sun for the required length of time. The flexible bag collapses flat for storage and at 4 ounces (105 g) is a very compact and lightweight treatment system for backpacking.

Spout and Handle
Spout and Handle

Note: SolarBag does not remove salts, so cannot be used for desalination.


The SolarBag looks like a typical wide-mouth, collapsible water-storage bag familiar to backpackers; in fact, it's a near dead-ringer for a Nalgene Cantene container, incorporating a compatible wide-mouth opening and cap. The only difference from my favorite in-camp water bag is the SolarBag lacks a pleated bottom to allow it to stand up (the difference relates to the treatment process described below). The bag is two-layer plastic comprising a puncture-resistant outer layer and taste-free lining. Inside the bag is the treatment media: two layers of plastic mesh enclosing a middle layer of open-weave fabric that keeps the mesh apart, presumably to maximize water contact. The mesh surface has various "nanotechnology-based" water-treatment coatings that perform the water sterilization, and it is this technology that sets SolarBag quite apart from a standard storage bag, or any water treatment device I've seen offered to campers and backpackers. Packaged with SolarBag are instructions, a fabric prefilter and marker dye to indicate treatment is complete.

Materials and Construction

The SolarBag is light and flexible while at the same time appearing tough. As with the Nalgene Cantene containers to which I compare it, the edges are welded and the plastic molded filler neck is likewise sealed with a welded seam. The screwcap is tethered to the pour-spout and can also be removed if desired. A reinforced carry hole on the top corner opposite the opening makes for easy pouring and toting. The spun polyester prefilter bag has an elastic opening and a loop to attach it to the SolarBag.


When exposed to sunlight, the coatings are said to break down or capture several types of water contamination, rendering safe drinking water in two to three hours (up to six in cloudy, cold conditions).

Prefilter can attach to the bag

Confession: I can only repackage and summarize the technical information supplied by Puralytics on the seemingly "magical" coatings performing the water treatment. Fortunately their website has a wealth of information, including numerous independent test reports for the curious and those better-educated than I. In addition to the lab testing, as of this BGT test the SolarBag has already notched several years of field use, including trials in the Third World.

Flat when empty, the filled SolarBag assumes a pillow shape and suspended in the middle is the treatment mesh, centered in a way that maximizes water contact. Treatment takes place on this mesh surface when exposed to sunlight. I emphasize that SolarBag is not a pasteurization system (i.e., relying on elevated temperatures to neutralize biological contamination with adequate time) and while warmth is said to speed the SolarBag chemical reactions, water need not be heated to a specific temperature for it to work.

Treatment is said to have these functional modes:
Photocatalytic Oxidation: an advanced oxidation process employing hydroxyl radicals produced at the surface of a photocatalyst activated by light.
Photolysis: the direct breaking of molecular bonds by light of appropriate wavelengths.
Photocatalytic Reduction: reduction of a contaminant to a less toxic state at the surface of a photocatalyst.
Photoadsorption: the light enhanced adsorption of contaminants to a surface.
Photodisinfection: using one or more bands of light to disinfect water.

Simple instructions

Fancypants terminology out of the way, what's it all mean? Harmful metals, including arsenic, lead, selenium and mercury are neutralized and adsorbed (captured) by the coating. An array of chemicals (hundreds are cited) are removed; the listing includes pesticides, solvents, water-soluble hydrocarbons, pharmaceuticals and explosives. The radionuclides cesium and strontium are likewise removed. (Not stated is whether the SolarBag can become a radiation source if it adsorbs enough cesium or strontium.)

Documentation & Instructions

Simple pictographic instructions are printed right on the SolarBag and a more complete instruction sheet is provided in the box. Far more detail, demo videos and in-depth technology discussions are presented on the Puralytics website.

Relevance to Backpacking

I don't (knowingly) backpack in places where these contaminants are a known hazard, but even in the mostly benign Sierra Nevada and throughout the mountainous West is a widespread mining legacy, with tens of thousands of abandoned (and working) mines. Some of these mines discharge metals, acids and other contamination yet, after 150 years. We also have widespread aerial spraying of pesticides that can make its way into source water. In short, one can never truly know the condition of one's drinking water source and technology that combines metals and organic chemical removal with biological purification ads a level of protection with virtually no extra effort or carried weight on my part.

Of greatest interest to me and perhaps most backpackers is treatment/removal of microorganisms: viruses, bacteria and protozoa. The U of Arizona reports SolarBag removed viruses and bacteria greater than 6 logs and removed/inactivated cryptosporidium greater than 3-to-4 logs, meeting "U.S. EPA Guide Standard and Protocol for Evaluation of Microbiological Water Purifiers." The test report notes that half the crypto removal was achieved by the prefiltering and half from the treatment itself. This reinforces the practice of always gathering the clearest water possible and prefiltering before treatment, and dovetails with my standard protocol.

Shelf and Service Life: SolarBag's stored lifetime is said to be seven years prior to first use. With a service life of 500 or more treatment cycles, I don't worry about wearing the bag out within that timeframe. (Unknown is whether raw water quality affects the effective lifetime but it's likely that it does, since adsorption capacity is finite lacking a renewal process). Given my 1-2 gallons per day per person water use estimate, I'd be hard-pressed to approach the limit during the predicted calendar lifespan.

Treatment media
Purification media closeup


Quite simple. Use of the prefilter bag is recommended when gathering water. For a first-time use in a new area, adding the indicator dye is also recommended to establish the needed treatment duration. Finally, for purification place the SolarBag on any flat horizontal surface exposed to direct sunlight, not shade. Do not hang or support it vertically. Once the dye is no longer visible, the water is ready to use. Presumably, one can dispense with the dye until conditions (water or conditions) change enough to warrant a retest. Per the maker, "Do not shake or twist a SolarBag as that can damage the integrity of the nanotechnology mesh." This means it needs protection when stowing it in a backpack.

Preparation & Packing

SolarBag needs no assembly so is ready to go from the box after an initial rinsing. The documentation cautions against folding the bag, potentially damaging the treatment mesh. SolarBag ships folded in the box so I guess the caution is to avoid creasing it, and it seems possible the coatings can be damaged by doing so.

I'm still left with a small quandary: what about very long trail days that end after sundown (or just an hour before, for that matter)? For now I believe a backup is probably warranted. In addition, as the treatment mesh inside the bag can be damaged, I need to find a safe way to carry SolarBag.


For a seemingly simple device the SolarBag is ambitiously complex. Considering the array of contaminants it targets and the simplicity of use it seems well-suited to the backpacker who doesn't relish fussy filtering, stirring a UV device or tasting treatment chemicals. Obviously, the required time versus bag volume and the direct-sun requirement come into play as to how many people one SolarBag can support, what locations accommodate its use and what seasons provide ample daylight. Hike with the filled SolarBag atop my backpack? That's the six-pound question, I guess.

Marker dye
Marker dye establishes treatment time

Field Report

Field Locations and Conditions

I carried SolarBag on two day hikes and two overnights in the Tahoe Sierra, then a week in Lassen Volcanic Park in the southern Cascades. Weather was sunny the majority of the time, but clouds and even light rain intruded four of those days. It was relatively warm, ranging into the 80s F (28 C) the warmest days while the minimum I saw in the early morning was right at freezing. Test elevations were between 7,000 and 9,000 feet (2,140-2,740 m) and given the June to August dates, solar radiation was essentially at its zenith for my sliver of the globe.

Lakeside Treatment
Sun and Water

I camped on a creek once and by lakes the rest of the time. I soloed the overnights and the weeklong trip was a party of three, which of course tripled water demands.


Mindful of the caution about folding or crushing SolarBag, I first cautiously loaded it next to or between soft or smooth items in my pack. Not always convenient, especially with a stuffed pack, but more or less do-able. Then, after a flash of the obvious and I switched to clipping it outside the pack using a carabiner through SolarBag's sturdy carry handle. Easy peasy! The sole downside is the occasional noisy flapping in wind, which I lived with. The outside hang also meant I can gather water and start treatment as soon as I rolled into camp, capitalizing on the available afternoon sun.

Gathering Water

With a visibly clear water source I sweep the SolarBag in the water to fill it. With cloudy or debris-filled sources, I use the recommended process of filtering with the provided bag while filling with a second container. A cookpot makes this fast and easy. While running streams had enough force to directly fill through the filter bag, still water does not and so the scoop method is needed. The filter accumulates quite a bit of visible debris, so is certainly worth using. It removes quite a bit more than fabric mesh prefilter bags I've used.

Adding Dye
Adding dye


Never had a problem finding a flat surface to lay the bag on but often had to keep an eye on shadows and move the SolarBag back into direct sun during treatment. It's also slippery and can slide off even gentle slopes. Other than that, using SolarBag is stone-simple: fill, add a dye drop, lay it down flat and leave it be. I found the dye bottle messy on day 1; going from my sea level home to the mountains the pressure inside builds and dye spurts out on first opening it, staining my fingers and presenting a challenge to dispense a single drop. Once pressure is equalized there's less mess.

When's it Done?

I'm in the air on how long treatment really takes because in the field the blue dye never was completely removed. The color would noticeably fade with time but even after many, many hours on a clear day at high altitude, where UV is high enough to sunburn the heck out of me in minutes, some blue remained. I drank the water; I shared the water; I cooked with the water; nobody ever got sick but I don't know quite what to conclude. Were all our water sources clean to begin with? Chances are pretty good they were. Is the dye a reliable proxy for complete treatment?

Dye color after a few hours
When will the blue disappear?

Volume Produced

Without more clarity on time to complete treatment it's hard to know how much water can be purified in a day. Sunny zero (non-hike) days make two batches (6 L) relatively easy and even three would seem possible assuming the 3-hour target can be achieved between sunup and sundown. Hike days, of course, limit treatment to morning and afternoon, when the sun angles would coincidentally mean less efficiency. There's no way I'm carrying it filled atop my backpack.

Even solo this means I need backup and with a party of three, SolarBag is a second water treatment device, not the primary.

Followup Test

After more than a week of testing I was in need of further insight. Back home I performed a little experiment. I took the SolarBag and a nearly identical Nalgene Cantene, filled them to capacity with 3 liters of water, put a drop of dye in each and left them on a sunny balcony. After about three-and-a-half hours I checked on them and found SolarBag had clear water. This was the furthest I'd seen it go in removing the dye, so represented a breakthrough of sorts. Interestingly, the dye in the companion bag was also mostly, but not completely gone.

Before photo
Treatment test start, control vs. SolarBag

What the heck?

After photo
Treatment test end, control vs. SolarBag

My home differs a few ways from the mountains: I'm at sea level for one, which lowers the sun's UV component compared to the mountains. It's a lot warmer here—by the time I ended the test the water was at body temperature. Third, I used tap water that presumably had no contamination whatsoever to treat and a bit of residual chlorine from the city water plant. It's also harder than very soft mountain lake water.

Whether these variables had any effect on my test is not something I can ascertain. I can only report that SolarBag visibly removed the dye and over in the control container, some other process reduced its dye, too. Visible dye remained, but much less than at the start.

And When there's No Sun, or No Time?

In considering extending SolarBag's utility when it's not actively treating water, I thought about what else it might do in camp. Pillow comes to mind, but only inside something fabric (it's slippery and won't stay put otherwise). I might yet press it into that if I don't carry something better. But what about making it part of a parallel or backup water treatment system? Now that it's clear SolarBag can't provide a group with all its water, how about incorporating it as part of a parallel or backup system?

Gravity filter
Connected to a water filter

I found a conversion cap that fits the bag with a hose connection allowing me to adapt a filter cartridge. Thus, SolarBag can be the raw water supply bag for a gravity system. Rig a way to hang it and voila, second use for SolarBag and no more sunshine worries.


SolarBag is what it promised in the Initial Report in so far as being light to carry and bone-simple to use. It's also well-constructed. I'm perplexed at the lack of complete dye removal in the field and then success back home. I also wonder why the dye diminishes in sunlight in a plain container, and whether it's truly representative of treatment completion. Without knowing more I feel restricted to giving SolarBag an "incomplete."

As a backpacking tool I consider SolarBag part of an integrated water treatment system and not a standalone solution. A stationary camper might be able to get enough water from one but hiking on the go takes a big hole out of the day when sunlight could otherwise be working to treat water. While I love its ease of use and vast list of contaminants treated, I also need more water in a typical day than it can produce when only mornings and late afternoons are available for treatment.

Long-Term Report

Test Location and Conditions

I took SolarBag on a four-day camping trip to Yosemite in late August. We camped at 6,000 feet (1,830 m) where temperatures ranged from the mid 40s to mid 80s F (7-30 C). Weather was clear and our site was partly wooded, allowing intermittent direct sunshine during the day—an important consideration for SolarBag use.


I ran daily tests using the potable campground water and found despite the intermittent direct sun, SolarBag was clearing the dye in less than three hours, a significant improvement from the Field Report results at Lassen. This may indicate the break-in we testers were alerted to does occur, and takes a number of treatment cycles. The treatment time improvement occurred even though LTR tests were at lower altitude, later in the summer and in broken sunlight—conditions that rendered the sun less intense than at Lassen or the Tahoe Sierra. I had expected dye removal to take longer, not less time. (Side note: no Yosemite bears bothered the SolarBag as it sat on our pick-a-nic table.)

After the final trip I rinsed and dried out the SolarBag then inspected it for accumulated wear and tear. While it now shows use I don't see any damage or signs of impending failure. The bag, its welded seams, carry handle and tethered cap are all fine. The printed instructions are perfectly readable and the treatment media inside looks intact. The prefilter needed washing to remove accumulated grime and shows greater wear than the bag itself. My observation is it will need replacement before the SolarBag itself wears out and I'm comfortable I can find an equivalent, either in town or through the distributor.


Positives: SolarBag is unique among the many water treatment technologies I've used. I love the ease of use and hands-off treatment. I value the wide swath of contaminants it's designed to remove and that it adds nothing to the water's taste. I also appreciate the light weight and freedom from field-repair or replenishment.

Drawbacks: Evaluated strictly as a backpacker's water treatment system I'm perhaps not dead-center in SolarBag's target demographic. Unless on a layover day I don't have the opportunity to catch the sun at its highest and I find late-day treatment iffy, getting the cycle completed by sundown. When I do have the needed time, the treated water is often quite warm, which is great for washing and not so great for drinking until it cools off. I also find it's not of sufficient capacity for a multi-person party and must be supplemented by at least one other water treatment device.

Future Use

Atypically, I don't yet know whether I'll adopt SolarBag for longterm backpacking use. Now that treatment cycle time seems to have shortened I want to give it another go next summer, when days are again long and altitudes are high. With my gravity filter add-on I think I now have a light and simple solution to the inherent dilemmas stemming from lack of sunlight or the presence of thirsty trail companions. I can hybridize my gravity filter setup by swapping in the SolarBag in lieu of the dirty water bag and hose, for a weight-neutral swap.


My grateful thanks to Puralytics and for the opportunity to test SolarBag!

This report was (mostly) created with the Report Writer Version 1.5 Copyright 2015. All rights reserved.

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