Find out how to install a whole-house water filter. Get tips on the best place in your house to install the filter, and learn about the maintenance involved.
LESLIE: Well, if you’re tired of that plastic water bottle going out with your recycling – or worse, in the trash every week – a whole-house water filter  might be a better option for you.
TOM: That’s right. A whole-house unit filters the water at the main just as it comes into the house, bringing you crisp, clean water from every tap in your home. To learn more, we turn now to This Old House  plumbing and heating expert, Richard Trethewey .
RICHARD: Hey there.
TOM: Now, Americans sure have an aversion to tap water but filtering it has to be better and less expensive than buying bottles. Are they difficult to install, these filters?
RICHARD: Well, it really depends. I mean you have to think about attacking water filtration in steps. If it’s a whole house, you need a large unit that’s going to handle all the water that’s coming through and in that case, you’re going to be going after the really visible impurities: dirt and rust.
RICHARD: When you think about the level of water you’re going to consume, you have to think locally. You have to think about a filter that’s going to sit underneath the kitchen sink to give you clean, beautiful water for both cooking and for your ice maker.
TOM: Well, that’s true. Because if you put it at the main, not only are you filtering your drinking water but you’re also …
LESLIE: Your bathing water.
RICHARD: And toilet water.
TOM: Yeah, exactly.
RICHARD: Yeah, yeah. So it’s – you really have to do it in steps. There’s a whole industry. It’s an industry that’s growing, because people are more and more worried about the quality of the water. “What happens if the bad guys touch the water?” They want to have some level of security in their house.
LESLIE: Mm-hmm. So how do you go about choosing one and then getting it installed?
RICHARD: Well, I think it’s – a dirt-and-rust filter is what you think about at the least case, at the water main coming in. And I think that’s going to be a function of local water quality . In so many parts in this country, the water is beautiful. We take it for granted in this country that the water is as good as it is. So, you may not need that.
But if you had an old, rusty main that’s in your old town or you had a galvanized water main coming in that was going to give you a lot of rust, you’re not – and you can’t change that new main to a new main, you might want to have a dirt-and-rust filter.
TOM: Now, what about a filter that goes actually at the tap? I’ve seen a wide variety of these types of filters. Sometimes you see the ones that screw on to where the aerator would go; other times, you see them to be large and fit inside the cabinet.
TOM: What’s the best way to approach that?
RICHARD: Well, I think there are two. All the ones that you spoke about – you know, the ones that go onto the end of a kitchen spout – they will usually include something called GAC – Granulated Activated Carbon. And water goes through this carbon and it cleans it up as it comes through. And so that’s at the least case, what you would put underneath the kitchen sink: either the little ones you see above the sink or the – these could be the ones that sit down in a canister, underneath, on your cold-water feed.
The other thing that people will put in is a thing called an RO – Reverse Osmosis. Now, that is a unit which will bring water through a membrane and with high pressure, it’ll push through this membrane so only the clean water gets through the membrane and the rest of the water. It’ll push through this membrane – the clean water – and the rest of the water will discharge to a drain, so it’s a lot more elaborate to install in that you not only have a supply but you have a drain. And people will complain that they’re wasting some water.
RICHARD: But the water level is clean and pure; it’s almost distilled.
LESLIE: Now, when it comes to changing the filters, does the amount of time between filter changes really vary to the type of cleaning system you have and where it’s located?
RICHARD: Well, it’s a function of water quality, again. Years ago, we had this filter that was so good it would clog up all the time and people hated it. But the water was perfectly clean, because it was taking every bit out of it. So it’s this balance point between taking out the important stuff but not having it be that you have to change it every month or every two weeks, you know?
TOM: But it is important to change it when it needs to be changed, because I remember in the 20 years I spent as a home inspector, I’d seen filters that folks put in with great intentions and then never touched it again for two years. And in fact, if you do that, I guess it could become unsafe.
RICHARD: I think it also becomes almost something you put on the list of when you’re going to change the batteries on smoke detectors.
RICHARD: It’s an annual thing. It should be the change of a season, we’re doing everything we’re going to do. As we hunker down for the winter, let’s get our smoke detectors in and let’s change the water filter .
TOM: Good advice. Richard Trethewey, the plumbing and heating contractor from TV’s This Old House, thanks so much for stopping by The Money Pit.
RICHARD: Glad to be here.
LESLIE: Alright. You can catch the current season of This Old House and Ask This Old House on PBS. For local listings and a step-by-step video on choosing a whole-house water filter and other projects, you can visit This Old House.com.
TOM: And This Old House and Ask This Old House are brought to you by The Home Depot. More saving, more doing. That’s the power of The Home Depot.