Yikes, living near industrial waste is quite hairy. I hope youâre not referring to the recent Ohio vinyl chloride spill. That whole watershed area might be compromised for years!
If you want the TL;DR: 6 stage, with a catalytic carbon filter in the 3rd stage if water has chloramine and an optional remineralizing 6th stage for taste and/or tolerance.
Keep in mind that, while this will be very detailed, there are still more details that I havenât gone over because they are rather technical and, IMO, not really that important. If you want to deep-dive into this, you can check out r/WaterTreatment.
1. In regard to the filter stages: 6 is about the max Iâd go (and what I have). Using more than that is very situational. To explain the differences, generally the order of the stages goes like this:
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1st Stage: Sediment Filter
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2nd Stage: Carbon Block
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3rd Stage: Another Carbon Block (or catalytic carbon)
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Usually another carbon block is added to further purify the water before the RO filter. These three stages so far are really to protect the RO membrane, since itâs the most imoportant step. Otherwise your membrane would be spent very quickly.
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Important note: Carbon block is different from catalytic carbon. Itâs a bit confusing - activated carbon isnât the same as catalytic, which is more reactive and can filter out more difficult organic molecules that traditional carbon cannot. If your water has chloramine in it, you need a catalytic filter in your 3rd stage (right before the RO membrane). Municipalities have been switching from adding chlorine to chloramine in tap water because it lasts longer. However, it is an irritant to some people, and just tastes plain foul if they overdo it. Most importantly, chloramine will eat away your RO membrane, so if your water test comes back with a relatively high level of chloramine, catalytic carbon will be a must.
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Service life 6-12 months
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4th Stage: RO membrane
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This, as the name implies, purifies water via reverse osmosis. Water after this stage should be near-pure. However, keep in mind that this will produce waste water. A portion of the water (gray water) is sent to your drain, containing all of the rejected contaminants. This water is mostly unusable for anything aside from flushing your toilet, so donât use it to water plants (they will die).
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Generally, in most models the wastewater:pure ratio is 3:1 (variable depending on your water pressure/quality), or 3 gallons waste to 1 gallon pure. However, the industry has been making it more efficient recently, and now you can see 2:1 or even 1:1 ratios. The newer all-in-one filters (which supposedly have all stages contained in a single filter) claim ratios of 1:2 or even 1:3, but the significant downside is that youâre locked into their proprietary filter system, which can get pricey. They also are powered units, so yet another electrical appliance that might crap out in a couple years. Personally, this is why I stick to traditional models that operate on water pressure, since I can repair and maintain them myself.
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Service life 2-4 years for the average US tap water, but can last even longer with soft water
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5th Stage: Carbon Coconut Shell Filter
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This stage is mainly for refining the water that comes out of the RO membrane or the storage tank, which can have an off-taste. This is why the all-in-one filters I mentioned before are being marketed, as they eliminate the need for this stage. Due to the purity of RO water, it can and will leach from its containers/pipings. Water after the RO step goes to a storage tank, where it usually sits for a while and accumulates this taste, thus the need to âpolishâ off this water before drinking it. When you turn on your faucet, the RO water passes immediately through this filter to ensure that it is back to being pure.
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Youâre probably wondering, why coconut? Well, itâs because coconut shells can achieve porosity even finer than a regular carbon block, which means more surface area to capture and bind stuff. Plus points for being renewable, I guess.
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Service life 1 year, or just replace it whenever your replace your RO membrane
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6th Stage: Remineralizing Cartridge
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This stage is an optional one, but still one that I recommend. Humans are not meant to drink pure water, as it can cause some people to have an upset stomach. Like I mentioned before, pure water can and will leach from its container, and when you drink it⌠well⌠you become the container. This may cause some of your own minerals to be lost to the RO water, but if you have a normal diet you shouldnât experience a mineral deficiency.
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What could happen, though, is a lot of stomach trouble. You see, pure water is not pH balanced (usually acidic), and itâs also hypotonic for obvious reasons. This usually gives people upset stomachs if they drink RO without any added salt or minerals, thus why you might want one.
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Service life 1 year, or whenever the water starts tasting different
Any more stages than this are just pure marketing. There is, however, a case for a 7th stage if you draw your water from a well. There would then be concern for microbial contamination, in which case a UV 7th stage would be needed. However, you get your water from municipal sources, so this is completely redundant unless your city really Fâs it up.
In a similar vein, make sure to follow the manufacturerâs guidance regarding sanitation. Biofouling is a concern once you get to a year and onward of service. A once-a-year cleaning with hydrogen peroxide should be sufficient beyond that.
2. In regard to testing your water: unfortunately, detailed lab tests are not affordable to most. Usually the lab tests start at around $150 for just the basic stuff. I was fortunate enough to be in a city that provided free testing and kits for certain contaminants. You should check if there are any programs/colleges/labs around your area like that. Just donât get the free testing from vendors or stores, as they will almost always try to find something at fault to sell you their own products.
However, as a basic test, you should look up our zip code on EWGâs database to get an idea of what youâre starting with. Then, get some pH strips and a cheap TDS meter from Amazon (no need for accuracy, just screening) so you can compare your input tap to your output RO water. This will let you see if your RO water has an alkaline pH and sufficiently lowered TDS level, at which point you can assume your system works.
The only unknown is whatever leaches into your water between your cityâs water facility and your house. There is a lot of aging pipe infrastructure, so thereâs really no way to tell unless you do a lab test. Personally, I would just test for things that you are most concerned with, be it lead, chlorine, PFAS. Or in Ohioâs case, dioxane tests because of the polyvinyl chloride. Also a test for chloramine if the EWG report doesnât show it, but you can also just call your municipalityâs water provider to see if they add chloramine (mine does), and then youâll know to get a catalytic carbon filter.
