I drank about 1 qt of cow urine and poo infested water last week before realizing something was amiss with my Sweetwater/MSR filter (looked like it hadn't even been filtered ie, silty). Finished the trip using my buddies.

I have an extra filter cartridge (older and used) and I thought I'd dye some water red w/ food coloring to see if the filtered water was the same color. Sure enough, the water came out red.

Does this mean this filter is ready for the garbage too?

The store closes in a couple of hrs so if there is much doubt, I need to buy another tonight. I'm leaving on another trip first thing in the morning.

That won't work, isn't an indication the filter is bad. Some old thread on that.

food coloring is molecular in size. Much smaller than what
filters filter, so trying to "filter" out color is not an indication that your filter is or is not working. If your filter has a "reactive" component that binds up organic compounds for taste improvement then color being reduced can indicate it is not exhausted, but it is no indication that a filter is doing it's job.

If the older cartridge isn't showing the black "webbing" pattern it's still good. Cleaning those filters entails scrubbing off a layer of the ceramic finish, and no more layers means the filter won't work. So unless you have frozen the filter at some point the older cartridge is likely still okay.

I'd call or email MSR on the malfunctioning filter and see what they say. There could be something else going on with the filter that doesn't have to do with the cartridge. I'm not familiar with how that particular model works (never had a sweetwater) but maybe there's an O ring or some other barrier to keep dirty water out of the chamber, and that's failing?

“Does this mean this filter is ready for the garbage too?”

No. The dye test is only for the First Need products. For the MSR products, some other method has to be used to see if it’s still OK.

-Barry

Thanks, all!

Considering what I drank ~10 days ago, I'm feeling pretty good about my immune system! If my old filter was allowing visible grit through, I'm guessing all the other nasties we're supposed to avoid was allowed through as well. I literally filtered from a major cow crossing in still water surrounded by cow poo. The whole area reeked like a commercial bovine feedlot. I might make myself sick typing this but it actually tasted good.