In today’s #SkepticalTuesdays post, I offer advice on water: to filter, or not to filter?

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Every now and then, I’ll see a post on my facebook page of someone buying something shiny and new for their home, and, being a good little consumer I’ll ask myself — do I need one of those? So when a friend of mine announced the purchase of a fancy water filter I stopped and wondered: “wait but why?”

The damn things, from the jugs to the little screw-on tap filters, have been ubiquitous throughout my surburban life. At a recent academic conference I might’ve been able to use one (the tap water was brown guys, and it wasn’t just a high level of iron — it ran clear after about five minutes… and the taste!). But for most of my life I’ve been sold, from a variety of sources, the benefits of filtered water, and I’m honestly not sure why.

Now there are plenty of people out there on the internet trying to get you to buy a water filter, which is why source analysis and critical reasoning are useful skills. Don’t, for instance, ask someone selling water filters whether or not you need one. Just like a car salesman will tell you that you need a car, and a sham-wow seller will tell you that you need a sham-wow, you already know what they’re going to say. There are some non-profits out there, mostly environmental activist groups, that might advocate for them too. They tend to (for obvious reasons) err on the side of caution/alarmism, but they shouldn’t be wholly discounted and should probably be dealt with on a case-by-case basis. For example, while it would probably be safer to never swim at a beach within 24 hours of rainfall (recommended by the NRDC here), in most cases that’s a bit of overkill. That doesn’t mean you shouldn’t be careful when the water smells funny, or when a health warning has been issued.

But, first things first: If you live in a city in North America, a typical one, one that treats its water in accordance with safety guidelines, adds fluoride for your teeth, chlorine to kill bacteria, and does testing on a regular basis, you do not need a water filter to be safe. No matter what the woo purveyors try to tell you, tap water is safe. It doesn’t have “memory” (and if it did, a filter wouldn’t help it forget all the poop that’s been in it). Fluoride is good for you in the tiny amounts added (and its absence is bad); and the chlorine added is in such tiny amounts (EPA recommendations are 4 parts per million) that they pose no risk to humans.

Tap water, in general, is fairly safe anyway — take the so-called “2010 Boston Water Emergency“: in May 2010, a seriously major watermain in Boston broke, leading to the use of backup open-air reservoirs. Because these reservoirs aren’t treated, they ordered a “boil water advisory” telling everyone the water wasn’t safe to drink without boiling it. But they did testing, which took a couple of days, and it came back that everything was well within safe levels. They were just being cautious, but even in the open-air reservoir water (with things like ducks hanging out in it) the contaminant levels were so low that it wouldn’t have been a problem. City drinking water is safe.

But not everybody lives in a place with great water. If your water comes from a well, for instance, you should be testing it in accordance with EPA recommendations. If you can’t be sure of your groundwater, yeah, you might need filters — especially if someone in your house is immunocompromised. At that point, though, you’ll probably want to talk to someone with expertise. Not all filters do the same thing. Some areas, for instance, have much higher fluoride levels than the 0.7mg/L in regular tap water — at 2mg/L you don’t want kids drinking it, and at 4mg/L you don’t really want anybody drinking it — so in that case you might want a reverse osmosis filter, because (repeat after me) an “activated” charcoal filter doesn’t remove fluoride. If you think there might be bacteria in your water supply, get that tested. And if you find it to be the case, maybe an ultraviolet filter would be what you need. Use evidence to make a determination about what’s right for you.

And then there’s the taste thing. Look, I get it. You think your water tastes gross. Maybe it does. Maybe you live in the dorms I was just staying in where the water tastes like it’s spent the last three weeks in a fire sprinkler system (this is exaggeration of course, because sprinkler water is black sludge). Maybe you have a super tongue that curses you with the ability to tell which of the Great Lakes a cup of water is from. Water itself is tasteless (although it can provoke taste based on what you last ate, like an afterimage), so if your water tastes like something, it’s probably what’s in it. If you’re really, really picky about what your water tastes like, I’m not going to tell you not to get a filter. But I will ask you to do one thing, first. After that, I’m totally cool with you spending a bunch of money on a fancy reverse-osmosis filter system just so your coffee will taste… well, let’s not get into that (I like almost all coffee — perc, drip, press, k-cup, pod — so my opinion on spending money on insane coffee machines is going to be predictable). But first, just that one thing:

Do an experiment. Buy a couple of kinds of bottled water. Use the same size glasses. Do a blind taste test. Have a friend pour them so you don’t know. If you can tell the difference, and you really don’t like the tap water, you’re good. If you can’t, you’ve just saved yourself the time and money to get a filter.

So the whole TL;DR is this: your tap water, if you’re in a major city, is probably just fine. If you live on well water, get it tested and react accordingly. If you don’t like the taste, make sure you’re not kidding yourself, and then, I guess, the rest is up to you.

Me, I’ll be drinking from the tap.

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Richard Ford Burley is a doctoral candidate in English at Boston College, where he’s writing about remix culture and the processes that generate texts in the Middle Ages and on the internet. In his spare time he writes about science and skepticism here at This Week In Tomorrow.