How Often to Change an Under Sink Water Filter? (Find Out Here)

Replacing the filters in your under-sink water filter is absolutely essential.

If you don’t replace the filters on time, the filters will become so clogged with contaminants that they’ll slow your water flow right down, or they’ll develop holes that allow trapped contaminants to leach back into your water. Old filters also have a much higher risk of bacterial growth.

You might already know the importance of changing your filters – but how often should you do it? When do under-sink water filters need replacing? And are all filters the same?

We’ll be answering all your pressing questions in this guide.

⌛ What’s the Lifespan of Under-Sink Water Filters?

If you’ve clicked on this guide, we assume you already know all about under-sink water filters and their wonderful benefits, so we’ll skip straight to the point.

The average lifespan of an under-sink water filter is 6-12 months. That means you’ll need to replace the filters approximately once or twice per year.

If you want to know what this is in gallons, that’s where it gets a bit tricky. The average under-sink water filter system has an average 500-1,000-gallon lifespan, but there’s no official correlation between gallons and months. So, a manufacturer might estimate that their 500-gallon filter lasts 6 months, but its actual lifespan could be higher or lower than this.

Replacing an under sink water filter

🆚 Under-Sink Filter Vs Whole House Water Filter Lifespan

Under-sink filters typically have smaller filter cartridges than whole house water filter systems. Having smaller cartridges means that there’s less space for the contaminants to accumulate on the filter’s surface, so under-sink cartridges need replacing more frequently than whole house water filter cartridges.

The filter cartridges in whole-house filtration systems have much longer lifespans of up to 10,000 gallons or more. However, whole house systems treat the water in your entire home, not just underneath your kitchen sink, so their water filters may only last a few months longer than the filters in an under-sink unit.

📑 Factors Affecting Under-Sink Water Filter Lifespan

How often should you change the cartridges in your under-sink water filter system? The exact lifespan of the filters depends on factors including:

The Filter Type

Most under-sink water filters consist of at least two, often three, different filter cartridges. Each filter cartridge is made from different materials, and each has its own lifespan.

Cartridge TypeAverage Lifespan
Sediment filter cartridge6 months
Carbon filters6-9 months
Post/ polishing filters12 months
Reverse osmosis membranes2 years
Filter type

Your Average Water Consumption

The amount of water that flows through your under-sink water filter will, in part, determine how long the filter lasts.

Let’s say you have a 500-gallon under-sink water filter. You live in a two-person household and you’re away at work during the day. You only use the water in your kitchen in the mornings and the evenings. Your water usage is going to be much lower than a family of four with parents who work from home and home-schooled kids.

In short, the more water you use, the more water that flows through the filter. And the more water that flows through the filter, the faster it becomes clogged with contaminants, and the more frequently it needs to be replaced.

Your Water Quality

Your water quality is another factor that affects the frequency of water filter changes required in your under-sink system.

Again, let’s say that you own a 500-gallon under-sink water filtration system, and your water’s TDS (total dissolved solids) count is low. The filter will become clogged at a slower rate because your water contains fewer contaminants that need to be removed. In comparison, a household with poor-quality water will need to replace their filters more often because they’ll become clogged with contaminants at a faster rate.

Water quality

So, the worse your tap water quality, the more contaminants will be removed, which clogs up the filter media faster.

📖 How to Know When your Under-Sink Filters Need Replacing

There are three key giveaways that your water filter needs replacing:

  1. Your water has an unpleasant taste. You probably purchased an under-sink water filter system to improve the taste of your tap water. If your water starts to taste unpleasant, it’s a sign that your water filters aren’t doing their job, and may even be leaking contaminants back into your water. Replacement filters are needed.
  2. Your flow rate slows down. It’s normal for an under-sink system to slow down the flow of drinking water from your faucet. However, the flow rate won’t slow to a trickle – unless a water filter cartridge in the system needs changing.
  3. Your water looks turbid. Dirty-looking water is a sign of a dirty filter. If you go too long between changing your filter cartridges, the filters may develop holes that allow trapped contaminants to leach into your water. Or they simply won’t have the capacity to hold onto any more contaminants, so your water will be no more filtered than it was when it entered the system.

✍🏻 How to Remember to Replace your Under Sink Filter Cartridges

Worried you won’t remember to change the water filters in your under-sink system? These are the best ways to remember.

Mark Your Calendar

If you’re the sort of person who wouldn’t remember any life admin tasks without a calendar of some sort, the best way to remember your filter changes is to mark your calendar.

On the day that you install your water filter system, check the user manual to see how long each of the filters lasts. Count up the weeks in your calendar and mark the date when the filters need to be changed. You could also mark a week earlier in the calendar to remind yourself to buy the new filters.

Marking the calendar

Set a Reminder

Often forget to look at your calendar? Set a reminder on your phone instead.

Your phone’s virtual calendar will display notifications to remind you of your important tasks and events. Make a note in your phone’s calendar to remind yourself to buy and replace your filters, and your phone will display the task on the day that it needs to be done.

Use the Filter Change Light

Your under-sink unit might have filter replacement lights that turn red when each of your filters needs to be changed. For people who struggle to remember monthly maintenance tasks, buying a system with filter change lights is a great solution.

Keep in mind that these lights are set on timers, so you should use your own common sense and replace the filters before the light turns red if you think you need to.

Under sink filter change light indicator

📆 How to Extend the Lifespan of Under-Sink Water Filtration Systems

Want to get more filtered water from your under-sink system before replacing the filters? Here’s how to extend your filter lifespans:

  • Only use filtered water when you need to. Don’t waste the water in your kitchen faucet by leaving the tap running while you wash up or using the water for cleaning or watering the plants. Try to only use your kitchen sink water for drinking.
  • Regularly clean or flush the filter. Some filters can be flushed to remove contaminants that have built up on their surface between buying filter replacements.
  • Install a pre-filter or water softener. If your water has harsh sediment or high hardness levels, these may be clogging the cartridges in your under-sink system. A self-cleaning sediment pre-filter or a water softener installed at your main supply line should tackle these impurities in your water supply.

🧠 Under-Sink Water Filter Lifespan FAQs

What happens if the water filter is not changed?

If a water filter isn’t changed, you’ll stop getting access to filtered water because your filter will become too clogged to work properly. Your flow rate will slow right down, contaminants may leak into your water, and bacteria may accumulate on the filter media.

How does the lifespan of under-sink water filters compare to other filtration systems?

Under-sink water filters have one of the longest filter lifespans of 6-12 months, depending on the filter type. Let’s see how they compare to the average lifespan of other filters:

  • Refrigerator water filters: The filter capacity of a refrigerator water filter is about 6 months
  • Faucet mounted water filters: Replace faucet water filters every 2-3 months
  • Shower filters: Change a shower filter every 6-12 months
  • Reverse osmosis membrane: Replace an RO membrane every two years

Do I need to change the water filter every 6 months?

It depends on the manufacturer’s guidelines, alongside factors like your water usage and how many harmful contaminants your water contains. The average lifespan of an under-sink carbon filter is 6 months. Contact the manufacturer if you’re unsure.

Can using an old water filter make you sick?

Yes. Bacteria can accumulate on an old filter, which is why it’s important to buy new filter cartridges according to the manufacturer’s instructions.