The advantages and disadvantages of portable water filters.
Advantages: a good inexpensive water filter will remove bacteria, parasites, and any particulate matter of the same or larger size. Disadvantages: filters that also remove viruses are significantly more expensive. The more expensive filters are limited in what other contaminants they can remove, such as lead, salt, VOCs (volatile organic chemicals), etc.
The most likely and most useful application of an inexpensive portable water filter is to filter out biological pathogens from a water source that is otherwise not significantly contaminated. For example, suppose that the power fails for a while (hurricane, earthquake, bad storm, etc.) and the local town or city water supply is contaminated with bacteria. They issue a ‘boil water’ alert. But you don’t have power yet, so boiling water has suddenly become much more difficult. An inexpensive water filter is a good option in this type of situation.
When you are filtering water, there are three sizes of pathogens that you want to remove:
(1) large: parasites and the larger bacteria
(2) medium: the rest of the bacteria
(3) small: viruses
So there are basically three size ranges of the pores in portable water filters, which can:
(1) filter out parasites and large bacteria;
(2) filter out parasites and all bacteria;
(3) filter out all parasites, bacteria, and viruses.
Some inexpensive filters will only remove parasites and the larger of the bacteria; these should be avoided. There are also some filters that remove only 99.9% or 99.99% of the bacteria. Not good enough.
The EPA standard for removal of pathogens is:
(1) bacteria, 6 logs (i.e. 99.9999%) or better
(2) viruses, 4 logs (99.99%) or better
(3) parasites, 3 logs (99.9%) or better.
“In 1986, EPA established the ‘Guide Standard and Protocol for Testing Microbiological Water Purifiers.’ This document provides a protocol for testing treatment systems that claim microbial purification of drinking water, specifically with regard to removing, killing, or deactivating bacteria, viruses, and protozoan cysts.”
“For bacteria…. minimum reduction of 99.9999 percent (6 logs) is required. For viruses…. minimum reduction of 99.99 percent (4 logs) is required. In the case of protozoans…. reduction of 99.9 percent (3 logs) is required.” (EPA.gov)
A log is ten times, so one log removes 90%, two logs removes 99%, three logs removes 99.9% etc. But why are there 3 different standards for removal of pathogens? Contaminated water may have a very large amount of bacteria, because pathogenic bacteria grow rapidly in water. So a high standard is needed. Viruses do not grow in water; they require a host. Pathogenic viruses, if found in a water source, are very unlikely to be found in the same type of quantity as bacteria. So a lower standard is all that is needed.
The types of parasites that afflict human persons generally require a host, and will die in the environment — except when in a cyst form. The usual suspects in this category are Giardia and Cryptosporidium. But in their resilient cyst form, they are not multiplying, so contaminated water will have a lower quantity of parasites than viruses or bacteria. The 3 log standard is sufficient.
Which portable water filters meet EPA standards for bacteria, cysts, and viruses? Not many. So far, the only ones I’ve found are the LIFESAVER Bottle and Jerrycan from LifeSaver Systems and the “LifeStraw Family” product from Vestergaard Frandsen. According to a company representative, LifeStraw Family will soon be available for commercial retail purchase in the U.S. If you know of any others, post in the comments below.
“The smallest bacteria are about 200nm (200 nanometers) in size, the smallest viruses are about 25nm. The holes in LIFESAVER membranes are 15nm so nothing is getting through.” (LifeSaverSystems.com)
How does the LifeSaver system compare to the EPA standard? It meets or exceeds the standard for cysts, bacteria, and viruses.
By comparison, the LifeStraw Family product “removes at least 99.9999% of all bacteria, 99.99% of all viruses, and 99.9% of parasites.” So both the LifeSaver and the LifeStraw products meet or exceed EPA standards. The LifeStraw Family uses a 20 nm filter, compared to the 15 nm filter of the LifeSaver system. But both appear to be highly effective.
The LifeSaver 4000 and LifeSaver 6000 bottles (named after the maximum amount of water they can filter) currently sell for under $200.00 on Amazon. (Prices will likely increase sharply, if/when demand increases sharply.)
In terms of cost per liter, any of these products is inexpensive. But they also have a limited shelf-life (while unused), a more limited lifespan after first use, and must be protected against freezing or the ceramic filter may crack.
The LifeStraw Family can filter up to 18,000 liters of water, but it is not yet on the market, so we will have to wait and see what the pricing is like. I suspect that the price will be very competitive.
Now if you are willing to sacrifice the ability to filter out viruses, effective water filters become much more affordable.
The “LifeStraw Personal” is a substantially different product. The filter has a much larger pore size of 200 nanometers (rather than 20 nm). It will NOT filter out most viruses. But it does filter out bacteria to 7 logs and parasites to 3 logs (meeting or exceeding EPA standards). Cost is very affordable, at around $22.95 (current price on Amazon, but subject to change). LifeStraw Personal will filter up to 1,000 liters of water. Similar products from other companies filter a much lower quantity of water.
Katadyn has a number of products with 0.3 micron (300 nm) filters, that will perform similarly to LifeStraw Personal. Again, viruses are not filtered out, but parasites and bacteria are removed. Some Katadyn products use a 0.2 micron (200 nm) ceramic filter, but the capability to filter out viruses is still lacking. The Katadyn products are more expensive than LifeStraw Personal, but less expensive than the LifeSaver bottles.
Some companies offer filters that only filter out protozoan cysts (e.g. Giardia and Cryptosporidium). Don’t bother with those products. LifeStraw Personal and any number of Katadyn products will filter out protozoan cysts and bacteria (to 6 logs or better).
More on this extensive topic in future posts.