The world's most in-depth and scientific reviews of gear

How We Tested Water Filters

Thursday May 21, 2020
We built a custom testing apparatus to test all of the filters side-by-side.
We built a custom testing apparatus to test all of the filters side-by-side.

Struggling on your quest for better tasting and cleaner water? To help, we bought the top water filters currently on the market and compared their performance side-by-side. We scored each filter in a handful of tests and picked the absolute best to win an award — even building a custom apparatus to control the amount of contamination in the water supply and truly test these products head-to-head. Keep reading to see exactly what we did to evaluate these products and how we scored. Alternatively, head on over to our Water Filter Review to see how each filter scored and which ones came out on top!

We used shavings from lead fishing weights dissolved in acid as our source material for the lead removal test.
We used shavings from lead fishing weights dissolved in acid as our source material for the lead removal test.

Lead Removal


Responsible for a quarter of the total score for each filter, our first metric assessed how competent each filter is at extracting lead from the water. First, we had to contaminate the water supply for each filter. We did this by — carefully — mixing a solution of vinegar and hydrogen peroxide, to create peracetic acid. We then used a razor blade to scrape slivers of lead off of a fishing weight and dissolved them in the acid, which was then added to the water supply for the filters.

Of course, we used all the necessary Personal Protective Equipment (PPE) and followed standard lab safety protocols when we did this, meaning you really shouldn't try to recreate this at home.

Do to the somewhat dangerous nature of the materials used in testing  Personal Protective Equipment (PPE) was worn whenever necessary.
Do to the somewhat dangerous nature of the materials used in testing, Personal Protective Equipment (PPE) was worn whenever necessary.

We then took a water sample from each filter as well as one from the supply and sent them to a water quality lab for testing. We scored each filter on the percentage of lead removed and if it mitigated the lead concentration to acceptable levels, as defined by the EPA. We also took the margin of error of the lab results into account when looking at the EPA standard, though none of our filters were remotely close to the standard — all models were either well above or well below.

We used both testing indicator strips and a TDS meter to measure the level of contaminants in the water.
We used both testing indicator strips and a TDS meter to measure the level of contaminants in the water.

Chlorine Removal


For our second metric, also worth 25% of the score, we judged how well each filter did at extracting chlorine from the supply water. We used chlorine bleach to taint our water supply and conducted two separate tests. The first test was with astronomically high levels of chlorine — on the order of 1000 times more chlorinated than the average pool. The second test was with more moderate levels of chlorine about 10 times as much as a swimming pool. We used both chlorine test strips and a Total Dissolved Solids (TDS) meter to measure the concentration in the water, though we more heavily relied on the test strips. We found that the results of the TDS meter weren't quite as repeatable as the test strips and tended to jump around.

This testing setup allowed us to use an isolated supply for each filter  to contaminate it as we pleased.
This testing setup allowed us to use an isolated supply for each filter, to contaminate it as we pleased.

Salt Removal


For our final impurity removal metric — again worth 25% of the score — we evaluated how well each water filter did at extracting dissolved salts. In this test, we used table salt as our sample salt, mixing it to the water supply until we measured a median concentration of 445 ppm on our TDS meter. We then ran this water through each filter and scored their performance based on the percentage of salt removed. We found the TDS meter to be a bit more consistent at measuring salt content, but we still took multiple readings and then took the median result to use in scoring.

Most of the filters came with their own dedicated faucets  but the faucet mount filters required us to get a generic faucet to attach them to.
Most of the filters came with their own dedicated faucets, but the faucet mount filters required us to get a generic faucet to attach them to.

Taste


Moving on past our trio of impurity filtering metrics, we looked at how the water coming out of each filter tasted. This metric is worth 15% of the total score and is comprised of two tests. First, we ran already purified water through each of the filters and had our panel rank and score the taste of each glass of water, without knowing which filter produced it. This test was to see if the filters imparted any negative or undesirable flavors to the water.

Next, we concocted a batch of exceptionally bad tasting water using a combination of chlorine bleach and table salt. We had our panel taste and score each water sample — and in most cases, promptly spit it out because it tasted so bad.

Continuing a trend  the Nanan again earned one of the lowest scores in our mineral removal test.
Continuing a trend, the Nanan again earned one of the lowest scores in our mineral removal test.

Flow


For our final metric, we evaluated and scored the flow rate for each filter. We used a 1-quart container and all of the filters were full at the start. However, we did include the time it took to refill the filter and for it to filter more water, if necessary.

Conclusion


For more information on how each product did when subjected to the above tests, head on over to our comprehensive water filter review. Alternatively, you can check out our Buying Advice guide for more background information on these products and a breakdown of the different types.