14 Reasons Why Your Water Filter Is Not Working As It Should

Almost half of all Americans filter their water before they drink it, yet most don’t know when their filter isn’t working or how to fix it.

Water filters that are correctly installed in a clean filter housing should work effectively. However, blockages in the filter or housing area, broken valves, or a dry filter can prevent your water filter from working.

Below is a complete list of all the reasons why your water filter is not working. And more importantly a step-by-step guide on how to fix each problem.

This article is for anyone who uses a faucet-mounted filter, filter pitcher, reverse osmosis system, ultrafilter or refrigerator filter, and whose water filter is not working as it should.

So, let’s get started.

1. Incorrect installation

This is probably the most common reason why a water filter doesn’t work. It may seem obvious but if your water filter is not installed correctly it simply won’t work!

Incorrect installation of a water filter most commonly occurs when an old filter is replaced with a new one. Usually, the water filter is not snapped, clicked, threaded or twisted all the way in. This then results in either water not passing through the filter or water leaking around the filter.

Simply remove the filter and re-install it – And be sure to follow any instructions specific to your water purification device and water filter.

2. Air blocked filter

Water filters, or the lines that feed them, can become blocked by air.

Air bubbles get stuck in the filter, which then prevents water from flowing through it. The tell-tale sign of an air blocked water filter is irregular flow. Although, in refrigerators and reverse osmosis systems a hammering noise can also indicate an air blockage.

Thankfully, air blockages are easily fixed.

For filter pitchers and water bottles, remove the water filter and soak in cold water, standing upright, for 15 minutes. Rinse under a running tap for 20 seconds and re-install.

For reverse osmosis systems, close your storage tank and flush at least 2 gallons of water through the system, letting the water run out the faucet.

For ultrafilters, simply open the flush port valve and allow a minimum of 2 gallons of water to flush through the filter.

For refrigerators, install your bypass plug and run water for at least 3 minutes to clear any air from the lines. Then remove the bypass plug and flush at least 2 gallons of water through the filter by pressing the dispenser button. For more information about refrigerator filter bypasses check out this detailed article.

3. Incomplete removal of packaging

Water filters can come with a superfluous amount of packaging and each layer of packaging MUST be removed before the water filter can be installed.

In particular, the protective caps covering the water filter must be removed before installation. If the protective caps are not removed the water filter cannot fit into its housing correctly and can’t snap into place.

Simple removal of all protective caps and packaging before installation of your new water filter will allow it to work correctly!

4. Filter has not been flushed

Almost all water filters should be flushed prior to their initial use.

Water filters are able to clean your water because of the material they are made of (often carbon) and because of their pore spaces. However, during manufacturing and shipping of your water filter, particles can become dislodged and block the pore spaces of the filter, preventing the water filter from working.

Some filter material coming loose during transport is extremely common and quite normal, which is why almost all manufacturers recommend you flush your water filter prior to use.

Flushing your water filter is straightforward – just run water through your filter. It is best to run a minimum of 2 gallons through your filter before drinking the water, although some manufacturers will recommend up to 5 gallons!

Once you have correctly installed your water filter follow the instructions provided below for your specific water filtration or purification system.

Filtration DeviceFlush Method
Faucet-mounted Filter– Turn the faucet on for a minimum of 5 minutes to flush the new filter
Filter Pitcher– Fill up the top reservoir
– Let it drain and discard this water
– Repeat the above steps at least twice
Refrigerator Filter– Place a container in the fridge’s water dispenser and press until your container is full.
– Discard this water and repeat until you have flushed at least 2 gallons of water through.
Reverse Osmosis– Empty your storage tank before installing the water filter
– Install the new water filter and turn on the reverse osmosis faucet
– Ensure the storage tank valve is CLOSED
– Allow several (3-5) gallons of water to run through the system and out the faucet
– Turn off the faucet and re-open the storage tank valve
– Allow the storage tank to fill with water
Ultrafilter– Open the flush port valve and the upstream water source
– Close the flush port valve after 20-30 seconds, and continue to prime the filter for 5 minutes (this will purge the filter of any trapped air)

And always remember to wash your hands with soap before installing your water filter so that you don’t introduce bacteria to your water filtration or purification system.

5. Blockage in the filter housing area

Replacing a water filter can cause debris to become lodged inside the filter housing.

Blockages of this sort are most common in filtration devices that require the water filter to be twisted into place. This is because debris gets caught in the threads of the housing. Although, blockages can still happen in any filter type.

To prevent blockages, clean the housing area thoroughly once you have removed the old water filter. Taking particular care to wipe along any threads or inside any slots.

6. Broken valve

A broken or faulty water inlet valve can make a water filter appear as though it is not working.

While faucet-mounted filters and filter pitchers won’t have this problem, broken valves are a common cause of water not passing through the water filters of refrigerators and reverse osmosis systems.

To check if you have a faulty valve:

  • Check your water pressure – if it is below 20psi, odds are it is too low for the valve (and water filter) to function properly
  • Check your water filter – if you recently replaced it, try re-installing the old filter and seeing if water runs through

So, if your water pressure and water filter are okay – it may be time to replace your valve.

7. Clogged filter

A gradual or sudden drop in the speed of water flowing from your water filter is a sign of a clogged water filter.

Over time water filters become clogged with the sediment they remove from your water. This is completely normal, but realistically you shouldn’t see your water flow slow down until the end of the water filter’s lifespan.

If the water filter is near the end of its lifespan and all of the pore spaces have become filled with sediment, then it is time to replace your filter.

However, if you have experienced a sudden drop in water flow and your filter is relatively new, then it is possible something has come through your water lines and clogged the filter. If this is the case you should remove your filter and potentially conduct a water test to see what that something is.

If you are on city water, then My Tap Score can test your water for you – click on the link below to get a test done today (affiliate link)

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However, completing a water test is more important if you use a domestic well for your water supply as it is more likely that the water could contain high amounts of Total Suspended Solids (TSS).

My Tap Score can help you out too, they will check for all the possible contaminants that could be in your well water.

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Either way you will have to install a new water filter, but knowing if something nasty has come through in your water will prevent you from i) drinking it and ii) repetitively replacing water filters unnecessarily.

8. Damaged filter

There are 2 contaminants in water that can cause serious damage to your filter.

  1. Sediment
  2. Minerals

1. The sediment that is suspended and carried by water becomes trapped when the water passes through a filter. Unfortunately, sharp, jagged and rough sediment or dirt can permanently damage the water filter.

If this is your problem then replacing your water filter is the only solution.

2. Mineral ions that naturally occur in water, and calcium and magnesium in particular, are often at high concentrations in water across the U.S. These minerals form scale (also known as lime scale) and over time these scale deposits build up, damaging your water filter.

Scale can become very expensive, as you will need to replace your water filter far more often than the manufacturer would normally recommend.

If you are unsure if you have scale or not, you can usually tell by a quick look at your water filter (or indeed around any surfaces in your home that regularly come into contact with water).

Scale is white and typically appears as a hard crusty layer. It can also look like corrosion. Unfortunately, removing scale from surfaces is surprisingly difficult and impossible from a water filter made of tiny holes.

Many water filters are designed to remove calcium and magnesium from water, just as many are designed to remove sediment. If you live in area with a water supply that has high concentrations of sediment or minerals then you may need to simply resign yourself to more frequent filter changes than you originally expected.

Alternatively, you could consider installing a pre-sediment filter to tackle sediment before it reaches your water filter. Or a water softener, if high concentrations of calcium and magnesium are the primary issue in your water.

9. Faulty new filter

A faulty new filter is probably the most annoying reason for a water filter to not work.

Luckily this doesn’t happen too often. Most new water filters will work just fine (once installed correctly).

However, to rule out a faulty new filter as the cause of your malfunctioning water filter:

  • Remove the new water filter
  • Clean the filter housing area
  • Re-install the old water filter

If the old water filter works, then remove it and replace it with the new water filter again. If the new water filter still doesn’t work, then odds are your new water filter is faulty.

Time to send it back to the manufacturer for a replacement!

10. O-ring, seal or rubber gasket not fitted properly

If you have any type of water filtration or purification system other than a filter pitcher, this could be the cause of your non-functioning water filter.

Faucet-mounted filters, refrigerator filters, reverse osmosis systems and ultrafilters all use either one or a combination of o-rings, seals and rubber gaskets in the filter housing area. If these sealing devices are not installed correctly the water filter cannot work.

Removing an old water filter to replace it is the usual cause of misplaced or incorrectly installed seals. When removing the old water filter it is often necessary to remove all o-rings, seals or rubber gaskets.

This is a good opportunity to clean the seals with soap and water and inspect them for any damage, with the slightest nick in a seal able to prevent the filter from working properly. This is because the rubber seal’s job is to get the filter air tight and to prevent leaks.

To ensure your o-ring, seal or rubber gasket is installed correctly:

  • Remove your water filter
  • Pull off the rubber gasket, seal or o-ring
  • Check for nicks, scratches or abrasions
  • Wash each rubber component separately and gently with warm soapy water
  • Replace the water seal or gasket – being sure to align it properly within the housing area and onto the filter itself
  • For reverse osmosis systems – you may need to apply a silicone lubricant to the o-ring before properly seating it in the groove in the housing area.

11. Dry filter

Most new filters need to be wetted before first use, and sometimes even before installation.

Dry filters will not work, and any water that does pass through is likely untreated, or at least incompletely treated.

The easiest solution for this is to flush your system as we discussed above, in point 3.

However, some water filters require soaking before installation. This is most common for filter pitchers or water filter bottles. To soak your filter:

  • Wash your hands with soapy water
  • Remove the water filter from its packaging
  • Soak the water filter STANDING in cold water for at least 15 minutes
  • Remove the water filter and hold in an UPRIGHT position under cold running tap water for 20-30 seconds.
  • The water filter is now wetted and ready for installation

12. Filter at the end of its lifespan

The sole job of a water filter is to remove contaminants from your water.

But doing a good job means that over time the available pore spaces of your water filter become filled and the water filter will need to be replaced.

This is why all water filters have a recommended replacement timeframe – and why it varies with your level of usage. The more gallons of water that passes through a water filter the quicker it will need replacing.

Most water filters need to be replaced every 2 – 6 months depending on the brand and your water consumption.

For example the Brita Standard and Stream Filter Pitchers should have their water filter replaced every 2 months or 40 gallons.

Whereas, my favourite water pitcher, the Epic Pure, only needs replacing every 6 months or 150 gallons (You can read more about the Epic Pure Water Filter Pitcher here)

13. Cheap no-name brand filter

When it comes time to replacing your water filter it is tempting to purchase a cheap no-name or aftermarket water filter.

It may make sense at the time to spend less money, but in the long run this usually ends up being more expensive than if you had just bought an OEM water filter.

OEM stands for Original Equipment Manufacturer, so an OEM water filter is simply a filter made by the same manufacturer as your water filtration or purification system.

Most manufacturers state in the users manuals to ONLY use OEM water filters. This is often more than just a recommendation, with use of a no-name brand water filter capable of voiding your warranty.

The primary issue with no-name water filters is that they tend to be an incorrect shape to correctly fit the housing area of your water filtration or purification system. Attempting to fit a no-name water filter can lead to leaks and damage to both the water filter and your system.

Investing in the correct water filter for your system will guarantee that you always have the right filter to fit your system and for clean water to flow effectively!

14. Water pressure is too low

Water filters and purifiers are designed to only work properly when the water pressure is in an optimal range. Water pressure that is too low or too high will prevent your water filter from working.

To complicate matters, the optimal pressure range varies between filter types and brands.

Some reverse osmosis systems will not work when tap water pressure is below 40psi, while some faucet-mounted filters can work with water pressure at 20psi, and some UV purification systems as low as 9psi.

Testing your water pressure is easy, you just need an inexpensive pressure gauge. I recommend this water pressure gauge from Amazon, it’s cheap and comes with a range of adaptors so you can test your water pressure at different locations both inside and outside your home – perfect!

Click on the image above to get one from Amazon (affiliate link) today.


Ultimately, if you buy the correct water filter for your system, carefully remove all packaging, clean your filter housing area and install the water filter as per the manufacturers instructions your water filter should work most of the time.

But for every other reason why your water filter might not be working, simply follow each of the step-by-step guides provided above to get your water filter working again!

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