Harmful Algae – Do Water Filters Work?

[Scott F.]

I was at a local lake yesterday packrafting (Lake Del Valle, California) and saw posted signs saying do not drink or cook with due to possible harmful algae in the water.  I know this is becoming more common throughout California with a few stories of serious health issues/death.   So, is it safe to filter such water to remove the harmful algae using a Swayer Squeeze or chemical treatment like Aquamira?

[Bill Budney]

A filter or chemical treatment will remove the algae, but not the toxins that they may produce. If it is important then you might consult a ranger about the specific type of algae and any toxins it may produce, but the safe approach is to avoid it, as the sign says.

[Ryan Jordan]

Here’s a previous thread about this.

There’s a bit of confusion about what you’re actually trying to treat/remove: the cyanobacteria (the organism most responsible for the algal blooms), or the cyanotoxins – the stuff that actually kills dogs, makes you sick, etc.

The concentrations of toxins are highest in the presence of cyanobacteria, because of toxins inside the cells.

So strategy #1: filter out the bacteria, and you tackle the bulk of the toxins.

But what to do when low levels of toxins remain dissolved in water?

It’s hard to say, there are a few issues here.

These are very hydrophilic (soluble) compounds so carbon filters aren’t great at removing them.

Chlorine has the potential to oxidize them into less toxic byproducts.

UV light, just based on chemistry, should do the same as chlorine.

Chlorine dioxide, less so because it’s not a strong oxidant against chemicals with this type of structure, even though it’s good at blasting the actual bacterial cells.

I think the strategy I’d use is to filter, then treat with UV. And only in an emergency. I wouldn’t take “normal risks” with algae-bloomed water.

I would definitely NOT use chemical treatment in the absence of filtration. That will destroy the cells, release the toxins, and now you have a soluble toxin concentration in the water that will be harder to remove/degrade.

[Paul Wagner]

Good advice here. I would just add that nothing clogs a filter quicker and more effectively than algae. Leave that water alone .

[Scott F.]

Thanks for all the advice and the link to the previous thread.  I’ll take the posted sign seriously.  Appreciate it.

[David Thomas]

While we’re talking about algae, I’ll pass on something I learned in my professional capacity a few years ago: algae can be carriers of heavy metals – arsenic and copper in the water-treatment system I was working with.  But unicellular algae are small enough to pass a 10- or 5-micron filter but, not presenting as metallic, don’t plate onto an RO membrane like metal ions do and therefore carry their metals into the concentrate discharge.  RO removes the metals from the permeate output (that you’d drink), but not from the concentrate stream.  If your filter removes bacteria, it should filter algae out, but it could clog quickly if the water is visibly greenish.

[Roger Caffin]

Cyanobacteria can produce several toxins which can be dangerous to humans and animals, such as geosmin. This is a (at least slightly soluble) molecule, not a particle such as a bacterium, and cannot be filtered out of the water.

Bottom line: Don’t even try to use this water. We (walkers) cannot make it safe.

Cheers

[Terran Terran]

https://www.berkeywaterfilterseurope.com/help/lab-tests/cyanobacteria-test-results

[Ken Larson]

SECOND Roger’s statement…..

Bottom line: Don’t even try to use this water. We (walkers) cannot make it safe!!

[AK Granola]

I see lots of video and photos of folks filtering water in New Mexico and Arizona from algae-covered cattle tanks. Is that a different type of algae that doesn’t create these toxins? It seems in many desert places, there is no other choice.

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