When’s the last time you changed your filter?

If you have a water filter pitcher sitting in your fridge right now, you probably don’t think much of it — just fill it up and you’re good to go, right? But when was the last time you changed the filter?

If you’ve been sipping on that Brita water because you can’t stand tap water and haven’t swapped in a new filter yet, we’ve got some news for you. Your filtered water may not be that pure after all.

In fact, it may even be worse than when it came from the tap. But before you freak out, here’s everything you need to know about water filter pitchers, and how to find out if you’re using them — and protecting yourself — properly.

“Different pitcher filters have different types of media in them, depending on the brand — most use activated carbon to reduce contaminants and impurities,” says Rick Andrew, director of the NSF International Global Water program. “Activated carbon works through adsorption, meaning that it attracts the contaminant molecules and they adhere strongly to the carbon.”

The large surface area of the carbon acts like a sponge that absorbs contaminants as tap water passes through. These filters remove:

  • metals like lead, copper, and mercury
  • chemicals like chlorine and pesticides
  • organic compounds that affect the taste and smell of water

For example, the Brita water filter pitcher uses a coconut-based activated carbon filter that removes chlorine, zinc, copper, cadmium and mercury.

However, activated carbon filters don’t remove all nitrates, dissolved minerals, or bacteria and viruses in water through the absorption process. Unlike metals, they pass through the filter because these don’t bind to the carbon.

That said, dissolved minerals in water aren’t necessarily hazardous and most tap water has already been treated to remove bacteria and other harmful microorganisms. So, it’s not usually a big deal if this stuff slips through.

Some filter types include a material called ion exchange resin which can remove “hardness” from water, or calcium and magnesium ions.

Water filter pitchers are an affordable, easy-to-use option for purifying your water, which is why they’re so popular. According to Consumer Reports, annual filter costs per year range from $32 to $180.

Ideally, your water pitcher filter label should indicate it’s NSF-certified, which means it meets certain standards for sanitation and efficacy. “Certification of filters lets everyone know the product has been tested and meets the requirements of NSF/ANSI 53,” says Andrew.

Other at-home filter treatments include reverse osmosis and distillation units, which are the most effective but also much more expensive and complex. These include things like refrigerator filters, under-the-sink filters, and even filtrations systems for your entire house.

When you need to change your filter depends on the brand and model you have.

“The most important thing for consumers to remember is that they really need to change those filters according to the manufacturers’ recommendations or they aren’t going to be effective,” says Andrew. “They are certified to reduce contaminants only according to the manufacturer’s instructions.”

The product instructions should tell you how long your filter will last. It’s typically measured in months or how much water has been filtered, usually in gallons. Some pitchers also have sensors that indicate when it’s time to swap in a new one.

Product and filter life

Here are examples of how often you need to replace the filter for five popular brands of water filter pitchers.

Brand and modelFilter replacement requirements
Brita Grand 10-cup pitcherevery 2 months or after 40 gallons
Zerowater 10-cup pitcherafter 25–40 gallons, depending on tap water quality
Clearly Filtered 8-cup pitcherevery 4 months or after 100 gallons
Aquagear 8-cup pitcherevery 6 months or after 150 gallons

These may vary slightly depending on how often you use the pitcher. But if we’re being honest, most of us probably aren’t diligent about replacing the filter every two months — let alone every 6 months… or every year.

An old filter is not only going to be less effective — and crazy slow — but also really gross and grimy. So, you’re putting yourself at risk for drinking whatever contaminants are in the tap water to begin with and whatever is growing (yes, growing) in that old filter.

“Filters that are not changed at the proper time may not work to reduce the contaminants that they were originally designed to address. If it’s not filtered out, that contaminant might result in potentially harmful health effects,” said Andrew.

As we mentioned, your water filter is not killing bacteria. Microbes can both be trapped and flow into your water, and it’s bacteria stuck in your filter that you should be worried about.

Yes, your old filter can add bacteria to your water

The moist environment in the pitcher filter is perfect for multiplication, so bacteria can reach higher concentrations. This can make you sick if you continue to use the old filter.

An older German study found that the amount of bacteria was less in tap water than filtered water after one week of use at two different temperatures. Researchers concluded that the filter had a biofilm growing on it, and in some cases the bacteria colony counts in the filtered water was up to 10,000 times those in the tap water. Yikes.

First things first: Tap water that hasn’t been filtered isn’t the same as untreated or “raw” water that you get from dipping your cup in a stream. This water isn’t safe to drink. But even treated water can still contain physical, biological, chemical, and even radiological contaminants. Where you live and where your water comes from — a well, ground water, city — as well as safety regulations and how it’s treated are all factors that can determine what’s lurking in your water.

Contaminants can be naturally occurring or caused by human activity. The list of junk that can end up in your drinking water is pretty extensive, according to the Environmental Protection Agency (EPA), and can include things like lead, pesticides, industrial chemicals, and other heavy metals. Some contaminants are harmless, but others can be harmful at high levels.

Lead poisoning can occur if lead pipes or faucets are used in your plumbing system, typically when they corrode. Poisoning can cause delays in development and learning disabilities in children. In adults, it can cause kidney issues and high blood pressure.

The only way to know if there is lead in your water is to have it tested, because you cannot see, smell or taste it, according to the CDC.

Biological contaminants include:

  • bacteria like E. coli and Legionella
  • viruses like norovirus and rotavirus
  • parasites like Giardia and Cryptosporidium

These can make you really sick, often causing gastrointestinal problems, such as diarrhea, cramps, nausea, and other complications. Tap water is usually sanitized to remove these but outbreaks can happen.

Again, these contaminants can be present in unfiltered, treated tap water or water that’s passed through an expired, ineffective filter.

Generally, you’ll know if the tap water in your area or a place you are visiting isn’t suitable for drinking.

Most tap water in the United States meets the proper sanitation standards and is safe to drink — with exceptions of course. But if you really aren’t sure whether tap water or water in your filter pitcher is safe to drink, there are a few ways to find out.

One way is to tell is by looking. Fill up a glass and see if you notice any cloudiness or sediment in your water. These may be signs of contamination and you either shouldn’t drink it or make sure it’s properly filtered first.

What if the cloudy water is from your water pitcher filter?

“If the filter remains in place beyond its lifespan, the water can become cloudy due to the impact of microorganisms that have colonized the filter,” says Andrew. “These organisms are typically harmless, but unpleasant, due to their presence in the filtered water.” But if you can’t tell for sure, it’s best to just get a new filter for your pitcher ASAP.

What if your water looks completely normal — how can you tell if it’s possibly contaminated?

“It is essential that consumers know what is in their water to determine if they need a filter,” says Andrew. “Local water utilities can provide a copy of their consumer confidence report, which details the quality of drinking water. People can also have their water independently tested so they can treat for specific contaminants if necessary.”

If you want to check the drinking water quality in your area, you can go to the EPA’s Consumer Confidence Report to find data specific to your area. This was established by the 1996 Safe Drinking Water Act Amendments that required states to do assessments of all public water systems.

You can also test your water quality at home. Your state or local health department may offer testing kits for free, or you can purchase them online or from a home improvement store. You can also have your water tested by an EPA-certified laboratory , or call the EPA’s Safe Drinking Water Hotline at 800-426-4791 for more information.

While it isn’t essential to have a water pitcher filter in your refrigerator, these carbon filters can help purify and remove a host of contaminants that affect the taste and smell of your water.

However, they won’t kill bacteria and if too much gets trapped in an unchanged filter, those microbes can multiply to levels that can make you sick.

So, if you can’t remember the last time you changed out your filter, it’s definitely time to do so. And if you love drinking from the tap, keep doing you. Happy hydrating!

Emily Shiffer is a former digital web producer for Men’s Health and Prevention, and is currently a freelance writer specializing in health, nutrition, weight loss, and fitness. She is based in Pennsylvania and loves all things antiques, cilantro, and American history.