Bad odors, mold, slow water or low pressure from your water filter are all signs you need to replace it. Water filters need to be changed regularly to prevent your water becoming more contaminated (rather than less) and to make sure your water doesn’t start to taste bad.
Filtered water can taste great! But knowing exactly when it’s time to change your filter is not always that obvious. Water filters have an expected life span (number of gallons or months of use), but these are usually “best case scenarios” and you may have to replace your water filter sooner.
11 Signs You Need To Replace Your Water Filter
1. Odor
Bad smells or odors, such as chlorine or sulfur (rotten egg smell), in your drinking water can come from a myriad of different sources.
But if your water filter is no longer getting rid of them, you probably need a new one.
2. Floaty bits or black mold
You have noticed “floaty bits” or black mold in your filtered water. Black mold is fungus that can cause many health problems.
If you find mold in your filtered water, you’ll need to give the whole water unit a good clean out (with disinfectants) and remember to replace the filter with a new one as mold spores will likely be in there too.
For extra precaution, make sure you wash your hands after handling your old filter as you don’t want to contaminate your new filter when you put it in to your system.
3. Slippery water
If your filtered water starts to feel slippery when you rub some between your fingers it usually means the water is SOFT.
If your mains water is normally soft (higher concentrations of sodium and potassium ions), but even after filtering it still feels slippery, then your filter is no longer doing its job and it’s time to be replaced.
4. Metallic taste or scale build up
You guessed it, HARD water. Hard water is caused by a buildup of minerals such as calcium and magnesium, which can leave a scaly build up on or in your water filter.
If your filtered water has also started to taste a bit metallic this is also a sign of hard water and its probably time for a new one.
5. Slow filtering speed
If your system is taking a lifetime to filter water when it used to be relatively fast, it’s likely getting clogged and ready to be cleaned or changed over.
For reverse osmosis systems, if the filters are old or not functioning properly it could take anywhere up to 6 hours to fill a standard sized tank. Whereas if the filters are new, then it should only take the usual 2-4 hours to fill.
Water Purification Guide has a complete troubleshooting guide on how to fix your water filter if it’s not working as it should available here.
6. High number of gallons used
This one is a bit of a no-brainer, but if the water filter in your household is being used heavily then you will burn through the filters a lot faster.
If for example you have a large family, then base how often you need to replace the filter on the number of gallons used and NOT the number of months it is expected to last.
7. High TDS in your filtered water
As water filters age they don’t work as efficiently as when you first bought them. By measuring the total dissolved solids (TDS) in your filtered water compared to the TDS in your unfiltered tap water you can see how well or poorly it is functioning. This can be done using a TDS monitor.
For reverse osmosis (RO) systems, as a general rule of thumb you can use the 80% rule as a guide on when to replace the filters.
The 80% rule means that if your RO water filters are still removing at least 80% or more TDS from your tap water then you don’t have to replace them. But if the filtered water TDS falls below 80% then you should look at replacing them.
For example:
If your tap water had a TDS of 100 ppm and your filtered water had a TDS of 025 ppm then the RO system is only removing 75% of the TDS from your mains water. As it’s below 80% removal then you need some new filters.
8. Low water pressure
You may notice that your under sink or reverse osmosis system is producing lower than normal tap water pressure. This may be a sign your filters have become clogged and need changing.
For reverse osmosis systems, if you have an installed pressure gauge and you notice the pressure drop, change your sediment filters straight away so you can keep using the more expensive carbon filters for longer.
9. Damaged water filter
Sometimes a water filter may become damaged and should be replaced immediately. Damage to a water filter generally occurs during installation, aggressive cleaning, or from not switching a system off during flushing, and some filters can wear out just through general use.
Damage can also be caused by hot water passing through the water filter. Its more of an issue for reverse osmosis membrane filters, which will have an upper limit around 95°F before there is membrane damage. Polyester or woven polypropylene are more easily damaged by hot water than wound natural string or cellulose types of reverse osmosis filters.
Water filters that are left to freeze can also become damaged. Typically, this occurs when an in-line filter, reverse osmosis system or under sink system is left with water inside it, which then expands during freezing.
This can damage the mechanical structure of the filters, and some damage you won’t even be able to see. Freezing can cause micro-cracks to form in sediment filters and carbon blocks leaving them ineffective.
10. Water filter passed its expiry date
The expiry date, or expected shelf life, of a water filter is there for a reason and going beyond it may increase the chances of being exposed to aesthetic impurities or potentially harmful contaminants in the water. Some water filters also contain chemicals that kill bacteria and going beyond the expiry date, even if you haven’t used it much, may increase your exposure.
In general, you will probably burn through a water filter faster than the expected expiry date anyway. This is because higher concentrations of TDS or total suspended sediments (TSS) in your mains water will shorten its life expectancy. Let’s face it, if you are still filtering water passed the water filters expiry date then it’s unlikely to be working at full capacity anyway.
11. Water filter indicator
Some water filters have made it MUCH easier by adding a built-in indicator that tells you when to replace it.
These can take a lot of the guess work out of it and are quite cheap and simple to understand. Here are some pitcher examples and what the indicator is… well… indicating:
| Brand / Product | Filter Replacement Indicator |
| Clear2o Pitchers with intelligent-filter indicator: – CWS100 – CWF500 | Color indicates gallons used: Green = 40 gallons Yellow = 50 gallons Red = Replace filter |
| Brita Pitchers with electronic filter indicator: – Wave – Capri – Space Saver – Marina | Colored blinking light indicates filter lifespan: Yellow = Nearing lifespan Red = Replace filter |
| Brita Pitchers with volumetric indicators: – Grand – Pacifica – Monterey | Colored blinking light indicates filter lifespan: Yellow = 32 gallons / 6 weeks – Replace soon Red = 40 gallons / 2 months – Replace filter |
| Levoit Pitcher with electronic filter indicator: – LV110WP-RF | Bars display remaining filter life %: After 60 days / 40 gallons bars are at the top (100%) and filter needs to be replaced. |
| Pur pitcher with LED indicator: – Pur Ultimate | Colored flashing light indicates filter lifespan: Green = Working Yellow = Change soon Red = Replace filter |
Related Questions
Do I really need to change the water filter in my refrigerator?
Refrigerator water filters are important for your chilled drinking water and ice maker. Refrigerator water filters include both mechanical and chemical components that need replacing just like your other water filters in your home.
Should a water purifier be switched off?
Water purifiers should be switched off during initial installation, cleaning, heading away on vacations, or if there are freezing water temperatures, hot water flows or a low water supply.
