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Bath Filters
If you don’t have whole-home water filtration, you might want a bath filter so you don’t absorb contaminants through your skin during baths. Here’s why most bath filters don’t work well, one that might, and two methods that you can try instead.
Why Bath Ball Filters Don’t Work Well
I am deeply skeptical that any brand of bath ball meaningfully removes water contaminants. Aside from the fact that some water will splash over the sides, here’s why: whole-house and under-sink water filters work on room temperature water, at a slow flow rate, and they’re built with a lot of filtration media. They remove a lot, but still not everything! Shower filters capture even less, because they’re dealing with hot water and a much higher pressure (read more here). The water coming through the bath spout is twice as fast as a shower, and these ball filters are even smaller than shower filters, so there’s less filtration media for contaminants to get stuck on. So, while these may capture a tiny bit, they’re more likely a waste of your money. Until I see testing with convincing results, I remain wary.
These filters don’t exist yet, and are still in the funding phase, but it appears that they are made of slightly more filtration media than most bath balls, and its design ensures that all the water is forced to go through it, not spill over the sides. They are planning to use KDF, which is an NSF certified copper-zinc mixture that is the gold standard for removing chlorine. I’d love to see testing on this once its released to see if it can truly remove chlorine effectively and at what percentage, with hot, high pressure water rushing through it! You can contribute to their kickstarter through this link or sign up to get updates from them.
If bath filters can remove anything, it’s chlorine. But guess what else works to remove chlorine? A pinch of vitamin C (ascorbic acid) powder. You can see the very exciting chemical reaction written out here. Adding a tablespoon to your bath water instantly neutralizes the chlorine, is safe, and inexpensive. It won’t remove any of the other contaminants in your water supply, but neither do most filters. And, reducing chlorine can mean less skin irritation and less lung irritation from breathing vaporized chlorine in. FYI, I’m skeptical that bentonite clay removes toxins from bath water like some suggest— while it does bind to toxins in the digestive tract, they’re flushed out of your body, and that’s how it’s effective. In this case, they linger in the tub, so I can’t verify they would truly do anything. It can also cause problems clogging your tub drain. Vitamin C causes a true change in chemistry.
Letting a shower hose dangle from your showerhead into your tub sounds silly, but it is effective! Shower filters have 2 advantages over bath filters. First, they have more filtration media (usually KDF) than any bath tub filter, meaning they can remove more contaminants. And, several brands have testing showing that they’re actually effective at removing chlorine for thousands of gallons— some are even verified to remove PFAS and other contaminants. See the shower filters I recommend here. If you don’t have a handheld shower with a long hose, spraying hot water from shower height may result in cold tub water, so I recommend unscrewing the shower head and popping a long shower hose on, like I do. I use the Weddell Duo filter and this hose.
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Click the bolded statements for links to research and more information.
What is KDF?
KDF stands for Kinetic Degradation Fluxion, and is simply a combination of copper and zinc. It is the gold standard for removing chlorine.
Do you absorb chlorine through the skin?
Chlorine can affect your health in two ways: coming into direct contact with your skin, and being inhaled into your lungs as a vapor from shower steam. With direct contact, chlorine can cause itchy skin and dry hair. Inhaling it is associated with lung and throat irritation, typically at the higher doses found in swimming pools, but sensitive individuals may notice it in a shower, depending on your water supply. Your skin does not absorb chlorine into the body very well, so this is less concerning.
Will bath filter removes lead?
None do, to my knowledge, and that’s probably OK. That’s because lead, bad as it is, doesn’t get into the body through water absorption by the skin. It also isn’t aerosolized into steam, meaning you won’t breathe it in. The main way lead gets into the body is by drinking it, which is why it’s important to use a water filter for your drinking water. So, be careful not to drink bath water if you have lead pipes. If you are still concerned, you can install a whole-house water filtration system that is certified to remove lead, or have lead pipe remediation done.
Can bath filters remove heavy metals?
No.
Here’s why: let’s say you have Arsenic in your water supply (as many cities do)— a KDF filter that advertises that it can remove Arsenic may sound like a good fit, but, it may only remove say, 1 molecule of Arsenic, once, in the first use. A larger activated carbon block that filters cold water moving through it at a moderate kitchen tap water rate can remove more, if pH conditions are right and other contaminants aren’t inhibiting it. A shower filter will remove far less because of the relatively small size (meaning smaller amounts of carbon), the hot temperature of the water, and the great force and speed it’s pushed through at, and a tub filter would remove even less. There simply isn’t enough time for the media to capture contaminants, and heat changes the ability for contaminants to bind to it, as well. A whole-house Reverse Osmosis system would be the only way to meaningfully decrease bathtub water levels of Arsenic.
Do you absorb arsenic from taking a bath?
No. Drinking water with arsenic is the main way it get into your body. Arsenic has poor dermal absorption, and while you can breathe it in from dust, your tub water would have to be 1,137°F for it to become aerosolized into steam for inhalation. So, prioritize removing arsenic from your drinking tap water instead. Some tub filter brands advertise they can remove arsenic, but this is likely just to make them appear more effective.
Can shower filters remove PFAS?
Yes, but only if they are tested and certified to be able to. The certification is NSF/ANSI 53, and you should also see results showing exactly how many PFAS were removed and for how long. Here is an example.
Can you absorb PFAS through your skin?
Unfortunately, yes.
Why are there so many misleading tub filter claims?
There is SO much healthwashing in the water filter business! My best guess as to why is three-fold:
Water contaminants are invisible, and often don’t have a detectable smell or have a color, so it’s very easy to claim more purification is happening when it’s really not. Self-testing your water is the best way to know if a filter is working, but it can be really expensive —running you hundreds of dollars to assess both before-and-after samples for heavy metals, PFAS, and other issues. Therefore, a company can get away with exaggerated claims. This is the most sinister of my guesses; that there is some level of deception happening for the purpose of making money.
Some brands may take legit, general facts about filtration media and retroactively (but inaccurately) apply them to their product specifically. Similar to the Arsenic example above, a good amount of KDF can remove heavy metals from water— there’s research on this. But if you put a teaspoon of KDF into a tub filter and run hot water on high pressure through it, it may not remove any! It’s context-dependent. So, I think some claims are made about the media filtration generally, but aren’t actually tested or verified for the filter itself.
Competition! If your filter’s “contaminants removed” list is shorter than your competition’s, it might look less effective to the untrained eye. If one brand is claiming it can remove a long list, then it perpetuates the spread of unverified long lists across brands.
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