The Upside of Under-Sink Water Filters

Installing, maintaining systems provide opportunities for plumbers.
The Upside of Under-Sink Water Filters
This two-stage standard under-sink filtration system has a compact housing that sits on the cabinet floor.

Interested in Residential Plumbing?

Get Residential Plumbing articles, news and videos right in your inbox! Sign up now.

Residential Plumbing + Get Alerts

Today, more and more households are having water-filtration systems installed in their homes. According to the Mintel Group, a global market research firm, sales of residential water-filtration products in the U.S. during 2014 totaled more than $830 million. That number is expected to grow over the next several years as more homeowners look to improve their water quality.

There’s a wide range of residential products available for filtering water, from simple faucet-mounted filters to whole-house systems. However, the fastest-growing products are under-sink filters, which also happen to be for many households the most practical, efficient and reasonably affordable system.

But before getting into the specifics of under-sink filters, let’s consider the role plumbing contractors can play in selling, installing and maintaining these systems so families can enjoy their tap water.

Job One: Educate

As mentioned earlier, there’s a dizzying array of water-filtration products available, and it’s often difficult for homeowners to decide which system is best for their home, family and lifestyle. That creates an opportunity for plumbing contractors to educate homeowners by presenting a brief, and objective, overview of the systems available.

By the time a homeowner consults with a plumber, they’ve probably already considered, and perhaps even rejected, the idea of using the three simplest forms of filtration:

  • Water-filtration pitchers are portable plastic pitchers that contain a carbon-spun fiber filter. Simply fill them with tap water and wait for the water to pass through the filter to obtain clean water. Water-filtration pitchers can remove chlorine taste and odor, along with some metals.
  • Faucet-mounted filters, as the name implies, attach directly to the end of the sink faucet to deliver crisp, odorless, fresh-tasting water. Most models have a carbon block filter that removes 99 percent of lead and trace levels of many other contaminants, including pharmaceuticals. A diverter allows the user to bypass the filter for times when filtered water isn’t required. 
  • Countertop filters consist of a plastic housing with attached faucet that sits on the countertop near the sink. Inside the housing is a multistage filter that removes 93 percent of dirt, rust, fluoride, aluminum, lead, iron and other metals. The filter attaches to the sink faucet with a length of flexible tubing. Tap water runs through the tubing, into the filter and out the gooseneck-shaped faucet. 

It’s important that homeowners realize the three options mentioned above offer the lowest level of filtration protection against tainted water.

On the other end of the spectrum are whole-house filtrations systems, which install near the point of entry and filter every bit of water entering the house. These systems start at about $400 for a bare-bones model, but can easily cost over $2,000 — not counting installation fees.

While these systems are very effective at producing clean water, it’s seldom necessary to filter water for use in the shower, toilet, washing machine or dishwasher, or for tasks such as watering the lawn or washing the car.

That brings us to under-sink filters, which strike a balance between effective filtration, simplicity and affordability. Most models require professional installation and maintenance.   

Under-sink filters

Under-sink filters are compact, super-effective systems that fit inside kitchen-sink cabinets. Tap water passes through one or more filters and travels up to a water dispenser mounted to the sink deck. The dispenser delivers pure, clean water for drinking and cooking.

Under-sink filters are available in several different models — and prices — to accommodate most households. There are two basic types of under-sink filters: standard (left) and reverse osmosis (RO).

There’s a lot to like about standard models: They cost less than RO systems, are easier to install, require less maintenance and take up little space inside the cabinet. However, they don’t remove as many contaminants as an RO system. A typical standard filter can remove particulates ranging in size from about 10-30 microns, which is pretty impressive. (A human hair is 75 microns thick.) RO filters are even more powerful, and typically have a filtration size of 0.0001 microns.

Standard under-sink filters can filter out sediment, eliminate chlorine taste and odor, and reduce levels of lead, bacteria, viruses, benzene and certain other chemicals.

One-, two- and three-stage models are available; each stage has its own unique filter. The more stages, the more effective the system. Standard under-sink filtration systems range in price from about $80 to $240.

Reverse osmosis systems (left) are similar to standard under-sink systems in that they have a series of filters and a top-mounted water dispenser. The main difference between the two types is that RO systems have a water storage tank that fits beneath the sink, and an RO system removes many more contaminants. If the storage tank doesn’t fit in the sink cabinet, it can be installed a few feet away, but that usually requires the installation of an auxiliary pump.

In the simplest terms, reverse osmosis is a process in which household water pressure forces tap water through a semipermeable membrane, trapping dissolved inorganic solids that would pass through standard water filters.

A typical RO system will remove sediment, chloramines, cysts, bacteria, viruses, lead, sodium, manganese, iron, fluoride, calcium and many other chemicals and contaminants. Most RO systems employ a four- to six-stage setup, and each filter removes specific types of matter and chemicals. Some even have an alkaline stage that restores alkalinity by adding small amounts of calcium and magnesium into the water. This stage is recommended when an RO system reduces the water’s pH by removing minerals. The cost of a reverse osmosis system varies widely, but on average ranges between $250 and $600 and can go much higher.

The parts that make up an RO system differ slightly from model to model, but here’s a list of the basic components:

  • Cold-water line valve: Fits onto cold-water supply line. Its flexible tube attaches to the inlet side of the prefilter.
  • Prefilters: Remove larger matter — like sediment, sand and silt — that could clog the RO membrane.
  • Reverse osmosis membrane: The heart of the system. This semipermeable membrane removes both aesthetic and health-related contaminants.
  • Storage tank: Pressurized tank that holds 2 to 4 gallons of water that has already gone through the RO membrane.
  • Postfilters: Carbon-based filters that remove any remaining unpleasant tastes or odors from the water.
  • Automatic shut-off valve: Stops the flow of water into the storage tank once the tank is full.
  • Check valve: Located on the outlet side, it prevents backflow of treated water into the storage tank, which could rupture the RO membrane.
  • Flow restrictor: Regulates the water flow and helps maintain the proper flow rate. It also maintains the proper pressure on the inlet side of the membrane.
  • Water dispenser: Every RO system has its own faucet that delivers clean, filtered water.
  • Drainline: Runs from the outlet side of the RO membrane to the sink drainpipe. It’s used to dispose of wastewater that contains the impurities removed by the system.

Installation of a standard or RO under-sink water filter shouldn’t take more than an hour or two, depending on the complexity of the system and the size of the sink cabinet. Expect an annual maintenance inspection to take about 45 minutes. Check with the filter manufacturer for specific information about routine maintenance and replacement parts. Homeowners are usually in charge of changing the filters, but you may have to teach them how to do it and how often to change them.

About the author: Joseph Truini is a nationally recognized home improvement expert who writes on a variety of home improvement and repair projects for The Home Depot. He is the author of numerous DIY books, including Building a Shed. To research water filtration systems, including the under-sink models, visit The Home Depot website.


Comments on this site are submitted by users and are not endorsed by nor do they reflect the views or opinions of COLE Publishing, Inc. Comments are moderated before being posted.