Water Treatment Plant Thurmont

A water treatment plant on Apples Church Road in Thurmont is shown on Monday.

Thurmont will, by Friday, distribute an advisory from the Maryland Department of the Environment regarding elevated levels of “forever chemicals” detected in the town’s water system, said Mayor John Kinnaird at a town meeting on Tuesday.

The chemicals, known as PFOA and PFOS, were detected by MDE in an October 2022 testing event, the results of which were shared with the town in mid-December along with a recommendation from the department to distribute an informational advisory regarding the chemicals.

(8) comments



If you have time, I'd appreciate your input regarding the filters we have.

They are Pentair / Pentek #P-250A. They are used in several dual housing under-sink systems. The NSF certifications were done using the Pentair US-1000 system.

The following is the most complete performance data I've been able to find so far:


The performance data is on page 9.

The P-250A cartridges are certified for reduction of MTBE, but for some reason that is not listed. MTBE *is* on the NSF 42/53 label on the filters, and Pentair does differentiate between the P-250 (not rated for MTBE) and the P-250A on their website. They both have the same 0.5gpm flow rate, but the P-250 is rated for 1,000 gallons (vs 500 for the P-250A)

Here is the NSF data:


Do a ctrl+F search for "P-250A[14] [Pb]"

Thank you!


Interesting, mrnatural. I use a RO system with a small on-demand storage tank that includes charcoal filters for my drinking water. A line goes from the system (in the basement rather than under counter to preserve the sparse kitchen storage space) to a faucet on the kitchen sink, with a branch to the ice cube maker in the freezer. The RO system does a better job than a charcoal filter alone. My replacement particle filters for the whole house are usually Pentek, depending on what MC has available. I try to get both string wound and PP filters that are at least 5 GPM to meet the water demand of the washing machine, dishwasher, shower, etc.

I don't bother treating the water used for washing dishes, flushing the toilet, or watering the flower beds. One area where there could be bioaccumulation is the water we use for the goats and horses, since that comes from a hydrant in the barn.


Thanks Gabriel.

RO is of course the 'gold standard' for water filtration. I was initially leaning that way. We ultimately decided against it in our situation (side of Catoctin Mountain, surrounded by RC zoned land) because:

* The RO water we've had literally stripped the saliva out of our mouths and left us feeling more thirsty. They may not all be that way.

* RO systems are (naturally) more complex.

* They are more expensive (although not by a crazy amount).

* They take more space, as you mentioned. Our kitchen sink cabinet is just 24" wide.

* Good quality "ordinary" filtration systems perform almost as well. There are several carbon filtration systems that trap PFAS.

When I bought this place in 1985, the water came from a *spring* just down the mountain. The previous owner had dug it out a bit so there was a few gallons reserve capacity and tossed a well pump in there on top of a cinder block. The health dept claimed it was fit for human consumption -- despite the frogs and salamanders living in there (seriously)...

So coming from that, anything is an improvement. [cool]

As far as I know, the Pentair/Pentek P-250A pair of filters is very good, but I have not been able to find the actual performance data sheets that list test conditions (water temp, flow rate, & pH); initial concentration of each contaminant; post-filter level, etc.

What got me to switch to the P-250A filters was looking at CR's water filter tests decades ago. Many of the systems used expensive proprietary filter cartridges -- like printer mfrs that price gouge on ink. One model however did very well -- it was top-rated and used standard 2-1/2 x 10" filters. It may have been Pentair's US-1000 and/or an "American Plumber" system. I found out that the system used the P-250A set, checked the performance data, and began using them in our existing under-sink dual housing (Sears Craftsman brand!) filtration system.

Like you, I don't filter any other water -- we get all of our drinking and cooking water from that spigot. I do use a Pentek DGD-5005 in the basement to remove sediment from all of the water. It is a 4 x 10" "dual-gradient density" filter made from spun polypropylene. It has a 50 micron pre-filter and a 5 micron post-filter.

A few years ago I bought a few string-wound filters -- 20 micron IIRC. That was a mistake. They allowed a large amount of sediment to get through and that obstructed a toilet valve and shower head, among other things. I can't recall the brand. Pentek string-wound may be fine. I've just stuck with the spun poly ones.


gabrielshorn2013 Feb 2, 2023 8:03pm

I get all of my water filters from McMaster-Carr, where I can put in the specifications and it shows me the products that meet those specs.


Thanks Gabriel, that's very helpful. [thumbup]

Of course I'm aware of McMaster-Carr and have ordered from them in the past, but I never got in the habit of using them.

I just took a look at their website, and man do they have the filters! These caught my eye (for use as a sediment prefilter):


I like the fact that they are reusable. Then I saw the price. $181 (for the 2.0 micron). OUCH. I'll probably stick with ye olde fashioned poly sediment filters.

I mistakenly clicked on these:


$92(!) -- but they do filter down to between 0.1 and 0.45 microns.

Moving on, I found these sediment filters, but the description only mentions NSF 61 (not 42):


The carbon filter I found has no NSF 53 rating, or any other rating:


There's a good chance there is some operator error on my part. Maybe I should be looking somewhere else, or using some filters?


The reported levels are high enough to be harmful based on adverse effects seen in test animals, at levels lower than are in the Thurmont drinking water now. The town will need to add filtration to their water treatment and it will increase the monthly water bills there. Necessary.


The end user can also add remediation to their drinking water system, such as reverse osmosis and an activated carbon filter. No use in treating water used to wash the car or water the flowers. Those contaminants have probably been there for decades, and are only noticed now due to the significant reduction in the threshold, and modern analysis methods. If it's in the town wells, it is in every private well in the surrounding area. We all share the same ground water.


Exactly gabriel.

I've been searching for possible replacements for our Pentek P-250A pairs of cartridges. I say possible because I have not been able to confirm whether or not they reduce PFAS by an acceptable amount. If I had to guess I'd say they do (their performance test data looks good), but I'd like to be sure.

In doing that search I've come across several systems (faucet mount, counter top, under-sink) that use carbon filters and are certified to remove PFAS.

People do not have to spend a lot of money on a filtration system -- although proprietary replacement filters can get pricey. That's why I prefer standard size (2-1/2 x 10" long) filter cartridges -- there are any number of mfrs to choose from. That said, there are many 2-1/2 x 10" "carbon" filters on the market that only have NSF 42 certification (taste & odor for those not familiar). Sometimes there is no NSF certification at all. It's definitely a "buyer beware" situation.


I get all of my water filters from McMaster-Carr, where I can put in the specifications and it shows me the products that meet those specs.

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