When is a filter not effective?

[Stephens]

I don't have much experience with personal water filters but I work in the water industry. I can see the taste advantages of chlorinating first and then running it through your filter to strip out the chlorine taste, but I will caution that doing it this way may not get all the viruses because they may be hidden/surrounded in such a way that the chlorine does not get to them. For municipal drinking water, the goal is to settle sand filter out as much junk as possible before you get to the chlorination stage so that any viruses that make it through the filter are at least exposed such that the chlorine will get them.

[dsuursoo]

Originally Posted by Stephens

I don't have much experience with personal water filters but I work in the water industry. I can see the taste advantages of chlorinating first and then running it through your filter to strip out the chlorine taste, but I will caution that doing it this way may not get all the viruses because they may be hidden/surrounded in such a way that the chlorine does not get to them. For municipal drinking water, the goal is to settle sand filter out as much junk as possible before you get to the chlorination stage so that any viruses that make it through the filter are at least exposed such that the chlorine will get them.

if you're going to try chlorinating before filtering, waiting an hour or two would give the chlorine plenty of time to do its magic.

[Stephens]

Originally Posted by dsuursoo

if you're going to try chlorinating before filtering, waiting an hour or two would give the chlorine plenty of time to do its magic.

What I was trying to point out is that chlorine can't do its magic if what it is trying to get to is hidden inside a clod of dirt or whatever else might be forming a protective layer around the pathogen. I may be paranoid but...

Water treatment is difficult because the things you are trying to remove or inactivate in the water all respond best to different methods.

A very good .3 micron filter is great at removing protozoa like giardia and cryptosporidium, but only decent at removing bacteria like ecoli or salmonella, and basically ineffective against viruses like hepatitis, rotavirus, etc. which can pass right through.

Chlorine dose and contact time required is highly dependent on the temperature and ph of the water but it is great at killing bacteria and viruses (ecoli is almost instantly inactivated by even small dose of chlorine), and good on giardia (might need up to an hour of chlorine contact time), but it would take days to kill cryptosporidium with chlorine.

So...to be safe, you need to do both filtration and disinfection. And personally I'd do the in that order. Or, use the one method that is totally effective against everything: Boiling for one minute (or a few minutes at high altitude).

[Bushwalker]

WHEN it comes to the risk of tar or other chemicals (adhesives, waterproofing?), coming off that tar paper used to line ponds in parks in some areas...

I don't know if i would be too worried about the risk of drinking a small amount of water that might, or might not contain a teeny amount of that relatively inert type of contaminat (when compared, say, to much worst toxins such as: pesticides, fertilisers or factory runoffs into rivers..) ~ IF I were only passing through, and filtered only a few litres??

IT would be a bit more of a worry if you were drinking that water regularly for several days in a row.

[Debkirk]

Wow. I have a doctor buddy who has a good background in parasitology . I took the time to take some water samples once and my filter killed all the (bacteria) bugs, but there are some viruses that it takes an antiviral pill to kill. So, to be on the safe side, I filter straight from the source into my Camelback using adapters that both the filter makers and the hydration bladder makers all sell. Then, I drop the correct number of purification tablets in the bladder.
Unfortunately even boiling does not eliminate some of the toxins (call it poison) found in water sources.
This doctor and I have both spent time in South America. He works in the Doctors Without Borders program, so I suppose he is the most informed guy I can find on this subject.
Failing this as a good answer, I would find a biologist who has a background in this field. Since 9/11, the USDA inspectors have become part of the Customs and Border Protection folks attached to the Dept. of Homeland Security. My dealings with them have always been informative. You might check with them.

[beekeeper]

I have read the same thing, that most filters will eliminate most bacteria, but not viruses. I have also read that the viruses in question were not a problem inthe US. I imagine they used to say the same thing about Africanized bees, fire ants, and Wesy Nile virus. Not a problem until it is...regarding other poisons, I suppose only distillation will get rid of the rest of it. I know I was told NOT to try to filter and drink from the Potomac and the Shenandoah rivers.

Originally Posted by Debkirk

Wow. I have a doctor buddy who has a good background in parasitology . I took the time to take some water samples once and my filter killed all the (bacteria) bugs, but there are some viruses that it takes an antiviral pill to kill. So, to be on the safe side, I filter straight from the source into my Camelback using adapters that both the filter makers and the hydration bladder makers all sell. Then, I drop the correct number of purification tablets in the bladder.
Unfortunately even boiling does not eliminate some of the toxins (call it poison) found in water sources.
This doctor and I have both spent time in South America. He works in the Doctors Without Borders program, so I suppose he is the most informed guy I can find on this subject.
Failing this as a good answer, I would find a biologist who has a background in this field. Since 9/11, the USDA inspectors have become part of the Customs and Border Protection folks attached to the Dept. of Homeland Security. My dealings with them have always been informative. You might check with them.

[Reality]

Originally Posted by beekeeper

I have read the same thing, that most filters will eliminate most bacteria, but not viruses. I have also read that the viruses in question were not a problem inthe US. I imagine they used to say the same thing about Africanized bees, fire ants, and Wesy Nile virus.

That's right. Most "filters" will not remove viruses (see similar post).

I like your thinking, beekeeper. The good news is that the viruses do not live long outside of a host. For the most part, these have only been a problem south of the equator. But, as you've alluded to, better safe than sorry (especially when the effort to do so is extremely easy).

Reality

[PBF Support]