Is an Under-Sink Reverse Osmosis System Worth It? Benefits, Costs, and Drawbacks

Carbon filters can make your water taste and smell better, but with RO you are getting much, much cleaner water than what that inexpensive Brita filter can muster. (That said, RO can’t capture everything, and carbon filters are still useful for capturing certain volatile organic compounds through adsorption. Most RO systems also have an additional carbon filtration system included.)

Note that two types of RO systems are available: Tanked RO systems filter water slowly (albeit passively, without electricity) and sequester it in a (rather large) tank under your sink. Today, tankless RO systems are more popular, processing water on demand but requiring electricity to keep things flowing expeditiously. Tankless systems are considerably more expensive due to their inherent complexity.

What Are the Real Risks of Contaminants in Water Today?

“US tap water is safe for most people most of the time,” says John Voll, an industrial water treatment veteran and the founder of Tap & Air, a website that monitors water and air quality for hundreds of municipalities. “The problems are local, not universal.”

The first step to understanding your personal risk is to gauge whether your own water is up to snuff by simply looking up its most recent data report online. The Safe Drinking Water Act requires community water systems to publish an annual report on the quality of water they’re delivering, due by July 1 each year.

These are heady documents, so to keep things simple, Voll says to keep your eye on three key pollutant metrics: lead, nitrate or arsenic, and PFAS (so-called forever chemicals popular in nonstick cookware and other products). While the first two are serious issues, they’re fairly rare today. PFAS, however, are a particularly significant problem across the country. Voll says that 98 of the 200 largest US cities have at least one PFAS compound detected in their water supply. Reverse osmosis systems can handle them—as well as lead and other compounds. Carbon filters usually can’t.

“Most people don't need RO,” Voll says, “but some households clearly do, and the way to tell is to read your own water report first.”

What Are the Drawbacks of Using an RO System?

RO systems come with a host of downsides, but most are related in some fashion to cost.

• RO wastes water: The particulars of RO technology have historically meant it requires a large amount of unprocessed tap water to create a small amount of purified water, sometimes up to 4 gallons or more of tap to 1 gallon of clean water (called the pure-to-drain ratio). In recent years that number has dramatically shifted, with 4 gallons of tap water producing up to 3 gallons of clean water, or a 3:1 pure-to-drain ratio.
• Filters are costly: RO systems can require up to six different filtration cartridges that must be replaced every year or two, depending on use. Much like printer ink, these costs can be easily overlooked when making your initial purchase. Plan to spend $50 to $200 annually on replacement cartridges, but check prices before you buy.
• RO can strip “good” minerals from your water: Calcium, magnesium, and potassium are all unable to pass through the RO membrane. RO systems also remove fluoride from your water, which many users may not desire and which dentists abhor. Some RO systems can remineralize water and/or raise the pH level of the processed water thanks to additional cartridges—but these, of course, mean further expense on replaceables.
• Plan for professional installation (and additional financial outlays): I try not to DIY too much when there’s even a remote potential for a water leak, so I get a plumber involved for installations like these. And since most RO systems require their own faucet, you’ll need to prepare to have a new hole drilled into your countertop for your tap if you don’t already have one available.

Do You Need an Under-Sink RO System?

Based on my analysis of my city’s water report, no I don’t really need an RO system, as there’s nothing hazardous to worry about. However, as the linked report notes, our water supplier uses chloramine as a disinfectant, and drinking that chloramine-treated water straight from the tap has a slight but noticeable, off-putting taste. This is exacerbated by the extreme hardness of the water; this part of Texas is basically built on top of nothing but limestone, and the resulting amount of calcium carbonate in the water can add a slightly bitter flavor, as well.

For me, RO is all about the way the water tastes. Any lingering contaminants that are removed along the way are just a bonus.

I tested the Waterdrop X12 for this story, hiring a plumber to remove a well-aged unit under the sink and replace it with this more capable one. The job was done in less than an hour.

Under-sink RO filters are separate from your existing plumbing, and most use three color-coded lengths of tubing to tie into it. One connects to your incoming water supply through an adapter valve, one clips into your wastewater drainpipe via an included fitting, and one connects to the faucet. I am confident I could have made these connections on my own—especially since I was replacing an existing system—but I’ve seen how even a small water leak can lead to devastating problems and was happy for the peace of mind that professional oversight supplied.