home

Last year, my co-founder Matt gave me a brain dump of a deep dive he did on water quality and purification. Until then, I had been using a water cooler since we have old water pipes and I wasn’t sure how clean our well water was. He sent over this initial list of resources:

• https://www.youtube.com/@waterfilterguru
• https://www.reddit.com/r/homestead/comments/kfpo2q/reverse_osmosis_for_well_water/
• https://www.nytimes.com/wirecutter/reviews/best-under-sink-water-filter/
• https://www.hubermanlab.com/newsletter/optimize-your-water-quality-and-intake-for-health

The Huberman podcast is a particularly comprehensive dive on the topic, and got me thinking I should look into under-sink water filters as an easier, healthier, and more cost-effective solution than a water cooler.

At-home water quality testing

The first step in the process is to do a water quality test, which will tell you what specifically you need to filter in your water. Wirecutter has a good guide on the various brands, and I opted for Tap Score’s Advanced Well Water test kit that looks for 114 factors in your water.

The process is very simple, and usually requires you to collect water first thing in the morning and return the container promptly for testing. Within a few days, I got my report by email.

You can choose to assess your results based on the EPA MCLs, which are federal drinking water standards, or HGL, which are much more strict and use the most extreme levels as determined by various states and academic institutions. By the EPA standards (left), there wasn’t much to worry about. But by the HGL (right), I had a few concerning results.

It turns out these results are relatively common for well water with copper pipes. Since my water is soft (low in calcium and magnesium) and slightly acidic (pH of 6.82), it’s corrosive and can increase the levels of heavy metals (like lead) in the water.

The coliform result is also common with well water — since the water isn’t treated, there can be bacteria introduced that can cause gastro issues. Tap Score has specific coliform tests that can go into more detail, but at this point I was ready to start deciding on a system.

Choosing a water filter technology

There are a ton of water filtration technologies and companies, and which you choose will depend on what you’re trying to treat. After researching, I found there were a few main categories:

• Chemicals: gasoline, herbicides, pesticides, etc.
• Radioactive: radon, uranium, etc.
• Biological: bacteria, viruses, etc.
• Heavy metals: lead, mercury, arsenic, copper, etc.
• Particles: microplastics, sediment, etc.
• Other elements that affect taste or smell

You can filter those in several different ways:

• Point of entry (i.e. where the water pipes enter your house, with several large filtration tanks)
• Point of use (i.e. under sink or countertop filters)
• Pitchers (i.e. the Brita pitchers you’re probably familiar with)

And those filters use several different technologies, each of which has pros and cons:

I knew I should focus on heavy metals and bacteria based on my lab report, but I also wanted something that would treat chemicals (who knows what pesticides leak into the well water?) and microplastics. I didn’t have immediate concerns about radon or my existing water’s taste or smell, but those end up being addressed by filtration anyway.

I also knew I wanted to focus on point of use (under our kitchen sink) instead of a whole home system. We don’t have space for one, and it seemed like overkill for our needs.

Based on the Huberman podcast above, I was already leaning towards a reverse osmosis system — you’ll read about it as the gold standard for removing most things you care about in water.

What is reverse osmosis?

On a high level, reverse osmosis works by forcing water through a semipermeable membrane that allows some molecules (like water) to fit through, while others (like chemicals or sediment) can’t. It’s the same osmosis process that helps water move in and out of our cells, except in this case it’s water moving in and out of a synthetic membrane in a water filter.

You’ll typically still put traditional water filters (we’ll get to these later) in front of the actual RO filter. This prevents larger molecules from clogging the more expensive RO filter and prolongs its lifespan.

The water coming out of the RO filtration step is extremely pure. Water purification is measured by TDS levels, or the amount of total dissolved solids. RO will reduce levels of water to under 25 parts per million (PPM). The only process that can get it lower is distillation, which requires heating water into steam and then condensing it back into water (and that’s to get from 25 PPM to 10 PPM).

After going through the RO filter, you’ll often add a post-filter to…add back some minerals. Weird, but we’ll get to that.

Clean water is stored in a small storage tank (usually 1-2 gallons) and the system disposes the waste water used during the RO process into your sink’s drain pipe.

So RO is very, very good. But if you read enough about it, you’ll come across some common concerns.

• Can reverse osmosis remove bacteria and viruses? Some manufacturers of non-RO systems claim RO isn’t effective at removing bacteria. Most RO systems will also not specifically talk about bacteria and say they must be used with “biologically safe water”, since bacteria can grow in the filter’s tight pores.
  
  The reality is more complex, and it helps to look up the sizing of the things we’re discussing. Giardia, which is a common water contaminant, is 10 microns. Bacteria (like E. Coli) are 0.1 to 1 micron. Both of those are easily stopped by standard carbon pre-filters, which we’ll discuss later. Viruses are smaller, usually 0.02-0.5 microns in size, but those are easily stopped by RO filters, which have 0.0001 micron pores. So if you keep your system clean, and regularly change the filters, the consensus is that bacteria and viruses shouldn’t be a problem. This was something I wasn’t 100% sure about, but I’ll be retesting my water to double check and may change my filter setup because of it (more on that later).
• Does reverse osmosis waste a lot of water? Unlike a filter system where ~all of the water that goes in comes out the other side, RO processes more water than it produces. The amount ranges based on the system, but usually it’s something like 4 gallons in, 1 gallon out. The unit I got was more like 1:1, which seemed ok. After digging into it, in actual usage this comes out to around 1-2 extra toilet flushes in a house per day, and I thought I could conserve elsewhere. Also, you can technically pipe the waste water to a containment vessel for use outside, which I may do eventually. Finally, the efficiency ranges based on the amount of water in the holding tank — it’s less efficient the closer it is to full. So I try to batch my water usage to deplete the tank as much as possible in one go.
• Is reverse osmosis water dangerous? You might come across people who say RO water is dangerous because of the lack of minerals. The argument is that RO water is missing minerals you need (calcium and magnesium) and that the pure water draws minerals out of your cells, leading to lower mineral levels in your body overall. The consensus is that this is really not the case. You get your minerals from food, and if you have a varied diet the mineral loss from RO water is pretty minimal. Plus, the RO systems I’m discussing have remineralization processes that add back in minerals after the RO step (mainly for taste, but it helps with this too.)

So essentially — you should get an RO filter.

Choosing a water filter brand

Let’s start with a few easy ones you shouldn’t buy. Brita is overpriced and ineffective (and not RO). Berkey filters are overpriced and inconvenient. You’ll think they’re the gold standard, but move on from both.

I was initially leaning towards Waterdrop or Aquasana, two of the more recommended brands on YouTube and Reddit. Waterdrop’s are interesting because they’re tankless, have a fast flow rate, and one of the best ratios of clean to waste water. Most RO systems with a tank are 1 part clean to 4 parts waste. Waterdrop’s is almost the opposite — 1 part waste to 3 parts clean.

The reasons I decided against these were:

• Proprietary refill filters: Most of the tankless units have proprietary cartridges, as far as I could tell. I didn’t want to be locked into a particular brand.
• Electricity: Waterdrop’s high-efficiency units require electricity, which I didn’t have easily accessible under my sink.
• Supply chain and provenance: Ultimately, I couldn’t find a great source about the quality of their filters. I was more comfortable with random RO filters, but because Waterdrop also remineralizes the water, I didn’t want random un-tested minerals being added. I found some third party lab tests, some of which cited dangerous levels of other chemicals being added.
• Affiliate marketing: Waterdrop does a lot of affiliate marketing for their reviews, so I wasn’t sure how real anything was. Ultimately, that turned me off.

My choice: Pure Water Products

After a lot of searching, I came across Pure Water Products, which mainly caught my eye because of its minimalist and utilitarian web design. But as I clicked around, I found the site to be such a happy relic of an old internet where people who are clearly obsessed about water could just write about, and sell, water stuff. Some of my favorite articles:

• The Pure Water Gazette, their newsletter about all things water
• Doulton bacteria filter test, where they filter lake water with a bunch of different filters
• Reverse Osmosis FAQ, where they answer a lot of questions I had about RO in general
• Reverse osmosis rejection percentages, with a helpful chart of RO reduction rates

They make all of their units in-house, and can customize anything because everything is just standard plumbing parts. The filters are also standard / non-proprietary, so I can get them anywhere or swap them out to try different ones over time. (Their full list of cartridges is very extensive.) I mean, here’s how they describe their RO unit:

Our Black & White Series Reverse Osmosis units have been sold and installed in the Denton area since the early 1990s and have been shipped to our out-of-town customers since the mid-1990s.

We’ve continued to improve our basic design, so that our Black & White unit is now the most easily installed and reliable standard reverse osmosis unit available anywhere. Instructions are short and precise; phone support is free.

Anyway, I was sold. The next step was to figure out which of their RO systems to order. Not only do they make any filter substitutions you want to their basic unit, they’ll customize the tank or parts depending on where you’re installing it. I had a few long email threads with dumb questions about various filters, and they were super knowledgeable about the pros and cons of different setups.

So, what did I end up with? The Black & White: 50/50 Series Reverse Osmosis Unit – 4 Stage, with the remineralization and pH balance package (with a few modifications). Specifically:

• Prefilter: Pentair Diamond Flow
  10 Micron Carbon / Sediment Filter (FC035)
• RO filter: Pentair GRO-50EN Encapsulated Membrane
• First post-filter: MatriKX CTO Plus (FC001)
• Second post-filter: Calcite Cartridge (FC018)

The 50/50 refers to the water saving properties of the Pentair RO filter, which is incredibly efficient (though still not as good as the top of the line Waterdrop models):

Our Black & White: 50/50 series units change the 4:1 ratio to a genuine 1:1. A gallon of product water goes into the storage tank for every gallon of reject water that flows to drain. This 50/50 performance is achieved by using Pentair’s exceptional new GRO membrane. With the GRO, greater membrane efficiency allows the use of less drain water to keep the membrane clean.

My further modifications were:

• Adding a test tap to the unit. As the owner explained to me over email, “if you get remineralizing membrane, ask us to build in a test tap (no charge for that) so that you can test the water before the post filter. Calcite in the post filter skews the TDS result so that you can’t really evaluate the membrane performance.”
• The Tomlinson Designer Faucet in cream

Gene from PWP said this would “make really good water”, and he was right. It tastes great, was easy to install, and has ~12 PPM TDS before the mineralization and ~25 after.

Moving forward, I want to try two filter changes:

• The Doulton Sterasyl ceramic filter as a pre-filter. The technology and history is pretty crazy, and it would help with the bacteria reading I originally got. As Gene said over email to me, “You can install a ceramic filter before or after the RO unit. There are pros and cons to both. If your water pressure is good, before is definitely better because it keeps the RO clean and you can ignore boil water alerts. I have one in front of my home unit and it works fine.”
• The Filtrex Greenblock Coconut Shell Carbon Block Filter as a post-filter, just to see if it affects the taste. “Coconut shell carbon blocks are said to produce water with a sweeter taste.”

And separately, I purchased one of their countertop water filters, which is also a good choice for city water or situations where you don’t want a permanent install.