Water Filtration Series: A Guide to Whole House Filters and Under Sink Filters

Clean water isn’t just a luxury—it’s a necessity. But with so many water filtration products on the market, the term “water filter” can mean very different things depending on who you ask. For the average consumer, a water filter might mean a faucet-mounted device or a refrigerator cartridge. For water treatment professionals, it could mean a whole-house filtration system designed to tackle iron, manganese, arsenic, lead, radium, chlorine, odors, turbidity, and much more.

In this first post of our "Water Filter Series", we’ll focus on one of the most common and widely misunderstood types of filtration: Filter housings with replaceable cartridges, used at both the Point of Entry (POE), whole house and Point of Use (POU), under sink. This subject can become very complicated but in this article we are going to focus on the most common filter housings and types of filter cartridges used in homes today. 

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What Are Water Filter Housings?

A filter housing is a durable container that holds a replaceable filter cartridge. These housings come in various sizes to suit different water flow volumes and contaminent removal applications. Common residential filter housing sizes range from:

• 2.5" x 10" slim line housings (for under sink use only)

• 2.5" x 10" standard housings (for under-sink or small whole-house filtration)

• 2.5" x 20" whole-house filtration (longer filter lifespan and higher flow rates)

• 4" x 10" whole-house filtration (longer filter lifespan, more filter options, higher flow rates)

• 4" x 20" Big Blue housings (longer filter lifespan, more filter options, higher flow rates)

When paired with the right filter cartridge. Cartridge filter housings can reduce rust, remove sediment, chlorine, odors, and even lead content in drinking water. But that doesn’t mean they’re always the best or most efficient solution for whole house filtration or even drinking water at the sink. 

Why are filter housings different lenghts!

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The Problem with Replaceable Cartridge Filters

Cartridge-style filters are widely available at big box stores, hardware stores, water treatment dealers, and for online purchase. They are often marketed as solutions for rust removal, sediment, chlorine, and even lead for the whole house. While replaceable cartridge filters can help, there are important drawbacks to consider:

• Short Lifespan: These filters clog quickly in poor water conditions, leading to frequent (and costly) replacements.

• Reduced Flow Rates & Water Pressure:  As filters become clogged, they reduce water flow rates and water pressure.  The finer the Micron rating for a filter cartridge the quicker it becomes clogged, reduces flow rates, and fails. 

• Limited Effectiveness:  Not all cartridge filters remove the same contaminants.  Some offer only minimal reduction of contaminents.  While other filter cartridges may remove a higher percentage of contaminents they become clogged much faster which leads to more frequent filter changing and can become very costly.  Historically, cartridge filters were more critical when wells drillers used steel well casings, which would rust and release scale into the water supply.  Today, most wells are drilled using PVC casings, sediment problems have declined—making whole house cartridge housings less essential in many homes.

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When a Filter Housing and Cartridge Filters Still Makes Sense

Despite limitations, there are cases where a simple filter housing and cartridge filter is a smart, affordable, and necessary, solution. 

For example:

• In Flint, Michigan, and many other cities around the US residents used block carbon filters, installed under the sink, to effectively reduce lead, turbidity, and chlorine in their drinking water until the municipal lead water lines could be replaced. 

• Many homes still have wells with steel casings that require sediment and scale removal. So a filter housing (with a replaceable filter cartridge) or a Blow Down style filter are still a necesssity.

• When a well is driven for a new home, or replacing an old well, sediment and sand can be a common problem. It is not uncommon to have sediment and sand in the water for up to a year  after the well was drilled.  Adding a whole house filter at the point-of-entry (POE) is frequently necessary to filter out any sediment or sand.  

• Another very important reason to have a whole house filter housing, is for sanitizing the plumbing system in the home. Plumbing in a home can be easily contaminated with bacteria in a multitude of ways. The well itself can have a high bacteria count   from insects and even mice getting in due to a bad well cap seal, a vent screen that has rusted away, a broken well cap, or a crack or hole in the well casing. More on this in future TWSB posts. The plumbing system in the home can also become contaminated by introducing bacteria before washing hands, faucet screens building up with debris (insects, bacteria, from the well).  Copper and galvanized plumbing are less susceptible to bacteria because of their natural bacteriostatic properties but it still happens, frequently.  Especially if a well has been heavily contaminated with bacteria, such as E-Coli. CPVC, PVC, and Pex plumbing (which is used in almost all new home construction now) all have a high probability for bacteria                            contamination from all the ways mentioned previously. If a home has any of these these plastic/pex plumbling types. I STRONGLY recommend having a whole house filter housing just to sanitize the household plumbing twice a year.  More on this topic in another Blog. 

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Alternative Sediment Filters: Rusco Blow-Down Filters

Another popular whole house solution for sediment issues in well water is the Rusco filter (aka blow-down filter). These filters contain a screen to trap sand and sediment and can be cleaned by opening a flush valve at the bottom - no cartridge replacement needed but they have a replaceable filter screen, which can last several years. Ideal for homes with sand intrusion or heavy particulate matter.

• 5" x 10" Rusco blow-down filter (for whole house use only)

• Maintenance: Blow down monthly. These type filters are commonly installed by well drillers and are excellent for extending the life of downstream water treatment equipment. 

• Blow Down Filter Housings: Have replaceable filter screens that are rated by micron sizes.

What's the difference between a spin down filter and a sediment cartridge filter? 

Choosing the Right Filter Cartridge for the Application

Filter cartridges vary by micron rating (the size of particles they remove) and contaminant-specific media (what they remove). Here's a breakdown:

➤ Sediment Filter Cartridge Types and Uses: 

Best for removing sand, sediment, rust, and large particles. Use cord-wound, poly-spun, or pleated filters in a 3" x 10" or 20" housing, or the best option is a 4" x 10” or 20" BB- housing.

• Fine Micron Filtration: 5 Micron   Fine particulate removal. Typically used in pre-filtration for reverse osmosis drinking water systems and in whole house series filtration. (available in polyspun or cordwound filament).

• Sediment Filters: 10–50 Microns Used for removal of sediment, reduction of iron and sediment pre-filtration for whole house and before water treatment equipment. (available in polyspun, cordwound, or pleated filament).

• DGD (Dual Gradient Filters): Dual gradient filters typically have a micron rating from 25-1 microns. 25 micron particulates, and larger, are removed on the outside of the filter and smaller particlulates are removed as the water progresses through the filter to 1 micron near the inside of the filter cartridge. DGD filters are used in 4" x 10"- 20" filter housings only.

➤ Carbon Filter Cartridge Types and Uses: 

Best for removing chlorine, taste and odor, for whole house (POE) and drinking water (POU). Use activated carbon for whole house (POE) in a 2.5" x 10" or 20" housing, or the best option is a 4" x 10” or 20" BB housing. For drinking water filtration at sinks use (POU) use activated carbon filters or a carbon block block filter in a 2.5" filter housing. (POU) housings can be directly connected to the cold water feed of the kitchen faucet to remove chlorine, lead, and VOCs. 

• Activated Carbon Filters: Clorine, taste and odor, VOCs, radon, removal and more. There are many types of activated cabon. EG: Coconut shell carbon (The most commonly used carbon), Granular carbon, Catalytic carbon, 
  

• Carbon Block Filters: Lead reduction, chlorine removal, VOCs removal, and heavy metals. 

• Chloramine Filters: Chloramines (a chlorine/ammonia mix used in city water) require specially-formulated carbon media. Not all carbon filters are rated for chloramine removal—always check NSF certifications for proper filter applications.

What is Activated Carbon?

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Maintenance Tips for Cartridge Filter Housings

Routine maintenance is essential for performance, heath and safety. Follow these tips:

• Replace filters regularly – Every 3 months or sooner, depending on water quality.

• Shut off water before filter housing and run water at a nearby faucet to relieve pressure before removing housing. If filter housing has a "Pressure relief button" hold it down until all water pressure is out of the housing, (make sure water is turned of before and after housing).

• Change the housing o-ring regularly – Use only food grade silicone lubricant (never petroleum-based lubricants like Vaseline).

• Clean housing threads, o-ring, lubricate the o-ring and clean the inside of housing with each filter change.

• Sanitize with bleach – A tablespoon of bleach in filter housing, rinse thoroughly. Helps prevent bacteria introduction from hands and helps prevent bacteria buildup from well water.

• Hand-tighten housing only – Never use a wrench to tighten filter housing. Tightening with a wrench/housing tool flattens and/or pinches the o-ring causing the housing to leak. Replace the o-ring if housing leaks after tightening.

• Bleed air after replacement – Use the pressure relief button or open a nearby faucet while repressurizing the filter housing to bleed off any air in the filter housing.

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Installation Best Practices

• Mount housings securely to a wall or bracket to protect plumbing.

• Install shutoff valves before and after the housing for easy isolation.

• Look for housings with built-in shutoffs and pressure relief buttons for convenience.

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What’s Next in The Water Softener Blog?

In our next article in the "Water Filters Series", we’ll explore whole-house filtration systems and water flow metered regenerating filters—the whole house solutions that tackle iron, sulfur odor, arsenic removal, and more at the waters point of entry (POE) to the home.

Stay tuned and subscribe to The Water Softener Blog for expert insights on making your water safe, clean, and trouble-free.

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I wish you, Good days and Good water!

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