That Sawyer filter looks interesting. Comparing it's specs to the LifeStraw Family specs, things don't make sense to me.
For one, how can a 0.1 micron filter (the Sawyer) claim to filter MORE bacteria and protozoa than a 0.02 micron filter (the LifeStraw Family)? It's pore size is 5 times larger. I
How can they claim? Because they have
lab reports just like the other guys to make claims?
I assume it has to do with the micron rating.
The absolute rating, of cut-off point, of a filter refers to the diameter of the largest spherical glass particle, normally expressed in micrometers (mm), which will pass through the filter under laboratory conditions.
The nominal rating refers to a filter capable of cutting off a nominated minimum percentage by weight of solid particles of a specific contaminant (usually again glass beads) greater than a stated micron size, normally expressed in micrometers (mm). I.e. 90% of 10 micron.
Micron Ratings: Absolute Microfiltration vs. Nominal
An absolute pore size rating specifies the pore size at which a challenge organism of a particular size will be retained with 100%
A nominal pore size rating describes the ability of the filter media to retain the majority of particulate at (60 - 98%) the rated pore size.
However there's microns and then there's MICRONS. These ratings are published by the manufacturers variously as "nominal," "absolute" and "average" or often, with no explanation. "Nominal" is the confusing one. To keep it simple, consider that this refers to the size of the largest pore in the filtering medium. However, organisms larger than this size will make it through the filter because they are not hard or rigid like ball bearings or needles, but rather can, and do, deform like gelatin or a sponge to get through. This leads to the "absolute" rating which means exactly what it says, it is absolutely the biggest critter that can pass through, period. This is the most accurate type of rating because there is no ambiguity. "Average" means that some organisms smaller than that won't pass, but some larger than that will and you have no idea what the limits are. Bear in mind that this is only part of the story since some filters utilize other methods to interdict and destroy smaller pathogens
2004
Nominal Rating - Expressed as a percentage of retention by micron size (For example, 90% of X Microns)
Absolute Rating - Expressed as the maximum sized particle which the filter will pass (All particles of X Microns size). A general rule of thumb is to multiply the nominal rating by 5 to obtain the more reliable absolute rating.
A leading water industry association defines nominal to mean 85 percent rejection at the stated micron rating and at the recommended flow rate.
Absolute provides a much stricter efficiency standard for the filter media, typically 98-99% percent rejection rate.
The ultra-pure water industry even defines absolute as a 99.99 percent (4-log) reduction, or greater.
However, independent validation might be in order for filter manufacturers making this claim.
What do you mean by 0.1 and .02 micron absolute?
Many other filters list nominal or average pore sizes which leave the possibility of harmful pathogens to pass through. By claiming absolute microns there are no variances in pore size on our filter membranes. At 0.1 and 0.02 micron absolute these are true barrier filters so there is no questionable time period whether the water is safe to drink.
So , always compare the percentages/log reductions, because that is what the lab tests proved.
Absolute micron is better than other microns, this explains the difference in lab tests.
Lifestraw does not advertise absolute micron (which means not-absolute), and the test results reflect this (they report different percentages)
See also
Re: Emergency water (gallons, EPA LT2 ESWTR )At its claimed 100,000 gallons, that little 4 inch Sawyer could supply an entire town for a multi-month emergency.
I assume the difference in gallons is the quality of the backflushing device. LifeStraw seems to use squeeze bulb, where as Sawyer provides a syringe; A syringe should produce significantly more pressure.
Thinking about it, this could explain the difference in the bacterial counts -- if one filter gets backflushed cleaner than the other -- the other filter will be scummier
For USA/Europe i would definitely go with sawyermini -- $25 at REI brick and mortar store
If worried about viruses, say you're filtering hospital sewage, then household bleach after filtering to kill the viruses -- only 13 minutes needed to inactivate viruses
see below
Table 9. MicroFiltration and UltraFiltration Studies Documenting Bacteria Removal Efficiency
Hollow Fiber Membranes
.2 and .1 can remove some viruses .
.03 has very good virus removal properties
North America vs. Third World Countries
In North America we do not have concerns about viruses in our water.
They simply cannot survive.
Viruses derive from contaminated human sewage and die shortly after entering a body of water.
In Third World countries outbreaks have occurred due to poor treatment of sewage.
Sewage without viruses can be handled by the PointONE™ filter.
The only viruses with the potential to survive in water are hepatitis (which is rare) and Polio (which is extremely rare).
You can contact CDC for information on virus outbreaks
in areas for which you are traveling.
CDC - Effectiveness on Pathogens - The Safe Water System
Inactivation of Viruses
12.72 Time of chlorine exposure (min)
0.5 Concentration of chlorine (mg/L)
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