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Don’t be fooled, choosing the best under sink water filter for well water is a lot different than for municipal water. Well water has certain characteristics that must be addressed with the correct filter. For example, if you’re battling the hydrogen sulfide beast – responsible for well water with a rotten egg scent – you need to choose the right filter. Simple carbon filters that work well for treating chlorinated municipal water aren’t enough.

In the comprehensive guide below, I share:

  • Top 6 Under Sink Water Filters for Well Water
  • Under Sink Water Filter Reviews
  • Tips on How to Choose the Best Under Sink Water Filter

System Description
#1) Express Water 11-Stage Alkaline Ultraviolet RO System

  • #1 Best Under Sink Water Filter for Well Water
  • The most complete under sink water filtration system on the market for well water
  • Sediment, Reverse Osmosis, Activated Carbon, Mineral, and UV filtration in a single unit
  • Includes 4-gallon holding tank & faucet
  • Life/Capacity: Filters & UV 6 – 12 months, RO Membrane 1 – 2 years
  • KDF-85 (for sulfur smell): No
  • UV Filter: Yes
  • Stages: 11
  • Service Flow Rate: .8 GPM
  • Dimensions: 19.5″ H x 15″ W x 5″ D (System), 16″ H x 11″ Diameter (Tank)
  • Weight: 30.2 lbs (shipping weight)
  • Further Reading: Express Water ROALKUV10DCG Review
#2) iSpring Boosted Performance Under Sink 7-Stage RO Water Filtration System

  • Significantly reduce wastewater and increase system efficiency w/ built-in booster pump
  • Eliminate up to 99.99% of microorganisms w/ UV filtration stage
  • See-Through Sediment Filter Housing for easy monitoring
  • Life/Capacity: Filters & UV 6 – 12 months, RO Membrane 1 – 2 years
  • KDF-85 (for sulfur smell): No
  • UV Filter: Yes
  • Stages: 7
  • Service Flow Rate: .5 GPM
  • Dimensions: 14.5″ W x 7″ D x 19″ H (System), 16″ H x 11″ Diameter (Tank)
  • Weight: 35.3 lbs
  • Further Reading: iSpring RCC1UP-AK Review
#3) iSpring 4-Stage High-Capacity Under Sink Water Filter (CU-A4)

  • #1 Best Reverse Osmosis Alternative for Well Water
  • Kinetic Degradation Fluxion (KDF) Media removes common heavy metals and helps to eliminate microoganisms
  • All-in-1 Multi-Layer Filtration from 5 to .1-micron
  • Life/Capacity: 6 to 12 months
  • KDF-85 (for sulfur smell): Yes
  • UV Filter: No
  • Stages: 4
  • Service Flow Rate: .5 to .9 GPM
  • Dimensions: 10.5″ L x 4.5″ D x 12.5″ H
  • Weight: 8 lbs
#4) HydroLogic smallBoy (36005)

  • Powerful KDF-85/Catalytic Carbon Filter (great for well water)
  • Massive 6,000-gallon filter life
  • Includes Sediment Pre-Filter
  • Life/Capacity: Sediment Filter 3,000 gallons, KDF Filter 6,000 gallons
  • KDF-85 (for sulfur smell): Yes
  • UV Filter: No
  • Stages: 2
  • Service Flow Rate: 1 GPM
  • Dimensions: 12″ W x 6″ D x 14″ H
  • Weight: 8.2 lbs
#5) APEC Water Systems Iron & Hydrogen Sulfide Filter (FI-KDF85-10BB)

  • Compatible with #10 Big Blue filter housing for a single-stage or multi-stage under-sink water filtration system (also compatible with all 10″ standard filter housings)
  • Specifically made for iron-rich well water and hydrogen sulfide removal
  • Life/Capacity: up to 20,000 gallons
  • KDF-85 (for sulfur smell): Yes
  • UV Filter: No
  • Stages: 1
  • Flow Rate: up to 4 GPM (service flow depends on the system)
  • Dimensions: 5″ W x 10″ H
  • Weight: 4 lbs
#6) CuZn UC-200 Under Counter Water Filter

  •  Note:  requires a sediment pre-filter for best results
  • Connects directly to your kitchen sink’s cold water line, no need to install an auxillary faucet
  • Bacteriostatic media protects against mold and bacterial growth over the long life of the filter
  • Life/Capacity: up to 50,000 gallons or 5 years
  • KDF-85 (for sulfur smell): No (KDF-55 only)
  • UV Filter: No
  • Stages: 3
  • Flow Rate: Existing
  • Dimensions: 4.5″ Diameter x 15″ H
  • Weight: 8 lbs

Best Under-Sink Well Water Water Filter Reviews

Have you chosen a winner yet? I know choosing the best under sink water filter for well water can get confusing. For this reason, I condensed my top picks to six systems to only include systems that actually work. Oftentimes, people on well water reach for the wrong filter after reading glowing reviews written by people on municipal water. In reality, there aren’t a ton of great under-sink filter options for well water outside of reverse osmosis. Well water filtration systems typically require a good sediment pre-filter at the point of entry no matter what under sink system you choose. I’ll explain that point in greater detail in the tips section below.

In this section, I share reviews for each system in my Top 6, along with the pros and cons of each system. If one of the reverse osmosis systems in the chart above caught your eye, scroll back up to check my previous review by following the link after the text “Further Reading.” Below, I share individual reviews for the latter four systems.

iSpring CU-A4 4-Stage UltraFiltration

The iSpring CU-A4 system is the best reverse osmosis alternative in my Top 6. It’s one of the only under-sink filtration systems that offer a standard KDF-85 water filter. One feature I really like in this system is the two stages of filtration that come before the KDF/Carbon filter. The first stage is a 5-micron polypropylene (PP) sediment filter that does the heavy lifting before your water enters the .1-micron UF filter. After the first two stages, the treated water then enters the KDF/Carbon filter where common well water contaminants including hydrogen sulfide are eliminated.

If you prefer a non-RO system that removes rotten egg odor caused by hydrogen sulfide, the CU-A4 is an excellent choice. Aside from hydrogen sulfide, the KDF + GAC filter helps to eliminate microorganisms that might be lurking in your well. While this filter is not a perfect substitute for a UV filter for microorganism elimination, it’s a superior filter compared to a standard carbon block or granular carbon filter.

Other highlights of the CU-A4 system include easy-twist on/off filter changes, no wastewater production, a space-saving design, and a 1-year money-back guarantee from a family-owned reliable water filtration company. To extend the life of the 5-micron sediment filter in this system – especially if there are larger particles in your well water such as sand – install a 50-micron or higher spin-down sediment filter at the point of entry.

  • No wastewater (reverse osmosis makes wastewater)
  • The filters are easier to change than an RO system
  • Delicious-tasting filtered well water
  • Transforms well water into bottled-water-quality water
  • A huge upgrade over a faucet filter
  • Easy-to-follow, step-by-step instuctions
  • iSpring customer service is top-notch
  • The auxillary faucet included with the system could be better
  • You might fall into the small group of people who don’t like the taste
  • This system is not made to significantly reduce TDS levels (choose an RO system for a significant ppm reduction)

HydroLogic Small Boy

The HydroLogic smallBoy system is one of a handful of under-sink filtration systems that include a KDF-85 filter standard. The smallBoy is a straightforward 2-stage system that’s excellent value for the money. Compared to more expensive systems sold by more well-known brands, this system by HydroLogic is an under-the-radar unit that gives you considerable bang for your buck.

Similar to the iSpring CU-A4, the smallBoy features a KDF/Carbon filter. Instead of granular activated carbon, the smallBoy blends catalytic carbon with its KDF-85 media. Catalytic carbon is a great choice for hydrogen sulfide removal, making this combination of catalytic carbon and KDF-85 the ideal choice for well water rich in hydrogen sulfide.

One of the greatest advantages of this system is the extra-long filter life of 6,000 gallons. HydroLogic recommends changing the sediment filter every 3,000 gallons and the KDF/Carbon filter every 6,000 gallons. The filter housing has a rated life of three years, and it’s probably the greatest drawback of this system. While the clear housing will get the job done, it’s inferior compared to industry-standard reinforced polypropylene Big Blue filter housings.

  • Simple installation (comes with tubing, connectors, valve)
  • A much better option than Brita and PUR filters
  • Tasty filtered water, easy to taste the difference after installation
  • Ample flow rate, the 1 GPM advertised rate delivers
  • Several leak reports
  • A handful of customer service complaints

APEC Water Systems Iron & Hydrogen Sulfide Filter (FI-KDF85-10BB)

If you prefer to customize your system and want to upgrade to industry-standard Big Blue filter housings, the APEC Water Systems Iron & Hydrogen Sulfide Filter is an excellent choice for well water. The filter is available in both 10″ and 20″ sizes to fit standard #10 and #20 Big Blue filter housings or any other standard filter housings. Personally, I like Pentek Big Blue housings. They stand the test of time and consistently perform well.

If you already have an under-sink water filtration system that’s not eliminating a sulfur scent, this filter can help to solve your problem. It performs best when used along with a sediment filter (such as a spin-down filter), a carbon filter, and a UV filter. What I like about this filter the most is that it’s 100% KDF-85, meaning you’ll get more contact time between your well water and the KDF media than a KDF/Carbon combo filter. Lastly, the rated filter life of 20,000 gallons is impressive. You might also want to consider using the 20″ size in a whole house water filtration system for well water.

  • A perfect addition to any well water filtration system
  • Effectively eliminates sulfur odor
  • Tasty filtered water
  • No more rotten egg scent at the kitchen sink
  • Approved for use with Big Blue filter housings
  • Reduced flow rate reports
  • A handful of reported longevity issues

CuZn UC-200 Under Counter Water Filter

It’s important to note that this filter is not made to filter well water on its own. Larger particles in well water such as sand will significantly reduce the life of the filter. Since one of the greatest advantages of this filter is its amazingly long life, the last thing you want to do is overload it. Having said that, this filter is one of the best single-filter under-sink water filtration systems on the market and works quite well with well water when used as a final stage.

In order for this system to function properly and deliver on its long advertised filter life, it needs a spin-down sediment filter before it, at a minimum. A better option is to install a point-of-entry whole house water filter before it. This way, the CuZn UC-200 is the final stage before the water enters your glass.

What I really like about this system is it connects directly to your existing faucet and won’t impact your existing water pressure. It’s great for drinking water and washing fruits & vegetables. If you like the idea of skipping an auxiliary faucet and want a high filtered water flow rate, this is the system for you. Just remember, it’s not designed to handle well water on its own.

  • Transforms well water into delicious, clean drinking water
  • Installation is quite easy
  • The convenience of filtered water straight from the existing tap is lovely
  • No noticeable change in water pressure after installation
  • Leak-free operation
  • Not recommded for hard or heavy-sediment well water as a standalone filter
  • KDF-55 instead of KDF-85 media

How to Choose the Best Under Sink Water Filter for Well Water

Since you made it this far, you know how important it is to choose the right types of filter media. Two integral stages for well water filtration are a proper sediment filter and KDF-85 media for hydrogen sulfide removal. Outside of KDF-85, an RO membrane works wells to remove everything from your well water, including hydrogen sulfide.

Below are the key components to look for in an under-sink system for well water:

  • UV Filter – Ultraviolet filters are a good chlorine alternative for destroying microorganisms that could be lurking in your well water. Since well water is untreated, harmful bacteria and other microorganisms can enter wells after flooding or snowmelt. Of all the water filtration components on the market, UV purifiers do the best job of eliminating microorganisms without chemicals. The combination of a reverse osmosis membrane and UV filter is a mighty effective one for treating well water.
  • Sediment Filter (5-micron minimum) – Well water often carries sediment including larger sand particles. A 5-micron filter is an absolute minimum for a 1st stage sediment filter in a well water filtration system. The iSpring spin-down filter is a great choice for removing 50-micron particles and larger before the water reachers your under-sink system. An inexpensive and easy-to-maintain spin-down filter will greatly extend the life of a 5-micron sediment filter and save you bucks in the long run.
  • KDF-85 – KDF-85 is the preferred media for hydrogen sulfide removal (*). Activated carbon alone won’t eliminate rotten egg odor caused by hydrogen sulfide in well water. KDF-85 is also a good choice for iron-rich well water. The bottom line is to choose KDF-85 for well water.
  • Reverse Osmosis – Reverse osmosis is an excellent choice for well water applications because of the extremely tiny pore size of an RO membrane (.0001 micron). Contaminants in well water and any type of water for that matter are no match for a semi-permeable RO membrane. The main drawbacks of an RO system are the wastewater created and the number of filters to maintain. A great way to reduce the wastewater volume is to choose a system with an integrated permeate or booster pump – or add one yourself to any RO system.

Those are the most important elements to look for once you identify what’s in your well water.

Bottom Line

Now you know the best under-sink water filters for well water and how to choose them. Beware of falling into the group of people who choose the wrong filter by reaching for a common activated carbon filter, or the other group of people who complain about the filter failing early because they expected a non-sediment filter to filter large sediment.

KDF-85 and reverse osmosis filtration are the two top options for well water. Get the extra peace of mind by choosing a system with a UV filter or adding one yourself to eliminate potentially harmful microorganisms. Happy filtering!

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