Will a filter cost me pressure?
Not when it is built for a whole house instead of a kitchen sink. Here are the three factors that decide it, the pressure Melbourne mains actually deliver, and how to read the gauge so a worn cartridge is never mistaken for a faulty system.
BlogPublished 31 October 2026By the Eco Purify Water team
In short.
With 20 inch housings and 25 mm ports, a filter takes a few kilopascals at household flow. You will not feel that in the shower. What you do feel is small housings and old cartridges.
Technically, yes: any filter puts some resistance in the line. The real question is whether you will ever notice, and three things settle that. How big the housings are, how big the ports are, and whether the cartridges get changed before they clog. Get all three right and you will not feel the filter in the shower. Get them wrong and you will know the first time two taps are running together.
When people complain about pressure after fitting a whole house filter, the cause is usually one of two things. Either the system was put together from 10 inch housings with 20 mm ports, which are under-sink parts doing a whole-house job, or a sediment cartridge has been left in for two years. Neither is a reason to skip filtration. Both are reasons to size the system properly and keep fresh cartridges in it.
Pressure and flow are not the same.
Static pressure is untouched. The filter only takes a little from moving water, and how much depends on size.
Pressure and flow are different things. Pressure, measured in kilopascals, is the push sitting in the pipe when every tap is closed. Flow is the number of litres per minute that come out once you open one. A filter has no effect on static pressure: with everything shut, the gauge reads the same. It only takes a little pressure while water is moving, and that loss rises with the square of the flow. Run twice as much water and the loss is roughly four times as large.
That is why housing size counts for so much. Make the cartridge twice as long and you double its surface area, so water passes through at half the speed and loses only a fraction of the pressure. On a whole house supply, a 20 inch cartridge is not an upgrade for the sake of it. It decides whether you feel the system or not.
Melbourne mains pressure, and the share a filter takes.
What the street supplies, the 500 kilopascal limit, and where a three-stage system fits within it.
Across Melbourne, mains pressure at the meter usually sits somewhere from 300 to 700 kilopascals, depending on your suburb and how far below the nearest reservoir or tank you are. Australian plumbing rules limit pressure at the outlets to 500 kilopascals, so houses at the higher end already have a pressure limiting valve. A filter installed downstream of that valve makes no difference to what it delivers.
With new cartridges, a correctly sized three-stage system loses only a handful of kilopascals at normal household flow, a few per cent of the street supply. That is exactly why the Eco Purify Home System is built on three 20 inch housings with 25 mm ports. The installed price also includes a pressure gauge, so you can read the drop for yourself instead of guessing.
Too small versus built for a house.
Three identical stages can perform very differently depending on the housings and ports around them.
| 10 inch, 20 mm ports | 20 inch, 25 mm ports | |
|---|---|---|
| Housing size | 10 inch housings, made for one tap or an under-sink unit. | 20 inch housings. Double the media, half the water speed, a fraction of the loss. |
| Ports | 20 mm (3/4 inch), frequently with reducing fittings that restrict flow even more. | 25 mm (1 inch), the same size as the main supply pipe into the house. |
| With one tap running | Generally fine while the cartridges are new. | No change you can feel. |
| Two showers and the washing machine at once | A drop you notice, particularly upstairs. It gets worse as the sediment cartridge fills. | Holds steady. The drop stays within a few per cent of supply pressure. |
| Cartridge life | Three to six months before the loading shows up at the taps. | Yearly for all three; sediment earlier if the gauge drops 70 to 100 kPa. The gauge tells you when. |
| Where they turn up | Budget kits and some systems supplied by plumbers. | Whole house systems designed for the job, ours included. |
Reading the gauge.
The gauge puts a number on the question 'is it time for new cartridges?'
Fitted on the inlet side, the gauge shows static pressure when nothing is on and dynamic pressure when water is flowing. The number that matters is how today's reading compares with the reading from when the system was new, both taken with the same tap open. Grit building up in the sediment cartridge adds resistance and pulls the dynamic reading down. Once it is roughly 70 to 100 kilopascals lower, that cartridge is finished, whatever the calendar says.
So the gauge tells you more than any fixed schedule can. A house downstream of mains works could fill a sediment cartridge in four months, while a house on a quiet, clean main could go fourteen. The carbon stages generally do not register on the gauge, so they are changed on time rather than by pressure. The Care Plan delivers the full set once a year, and our plumber checks the gauge while fitting it.
What the bypass valve is for.
Cartridge changes, servicing, and watering the garden.
A bypass valve sends water around the filter instead of through it. It exists for cartridge changes and the occasional housing service, so your home is never left without water. It is also the first place to look when pressure drops suddenly. A bypass left half open after a cartridge change, or an isolation valve that was not fully reopened, is the most common reason for a sudden pressure problem that gets blamed on the filter.
Some owners plumb the garden from the unfiltered side of the bypass. Irrigation uses more water than the whole inside of the house put together, and none of it needs filtering. Taking the garden tap off before the filter keeps all that water out of the cartridges, so they last longer.
When pressure does fall.
Five common patterns and the usual cause behind each.
- Pressure dropped the day the system went in: make sure the bypass and isolation valves are fully open, then ask the plumber to check the housings are seated properly and the cartridges are the correct size.
- Pressure has eased off gradually over months: the sediment cartridge is filling up. Compare the gauge with its day-one reading and replace the cartridge.
- Pressure fell sharply after mains works in your street: those works sent a burst of sediment into your cartridge. Replace it early.
- Pressure is low at only one tap: the problem is that tap, its aerator or its flexible hose, not the filter. A filter treats every outlet the same.
- Pressure is low everywhere, even with the bypass open: look at the street supply or your pressure limiting valve. Call your water retailer or the plumber.
Common questions.
Plain answers, ready to use.
Is a whole house filter going to reduce my water pressure?
Not in a way you will notice, if it is sized correctly. A system with 20 inch housings and 25 mm ports loses a few kilopascals at normal household flow. The complaints come from undersized 10 inch systems and from sediment cartridges that have clogged.
Does a filter change the pressure in my pipes when nothing is running?
No. With every tap shut, pressure is the same on both sides of the filter and matches the street supply. A filter only takes pressure while water is flowing, and how much depends on the flow rate and the state of the cartridges.
How big should a whole house filter be for a family home?
For a typical Melbourne house on a 20 or 25 mm main, three 20 inch by 4.5 inch housings with 25 mm ports. Anything smaller copes with one tap but falls short once two showers are running.
How can I tell whether a blocked cartridge is behind my low pressure?
With a tap running, compare the gauge to the reading from installation day. If it has dropped by 70 to 100 kilopascals, the sediment cartridge is spent. If opening the bypass brings full pressure back, the cartridge is your culprit.
What does the filter do to my hot water system?
Nothing bad. Your hot water service gets filtered water, so sediment no longer settles in the tank or on the element. Flow to the hot taps stays the same because the system is sized for the whole house.
Keep exploring.
The system itself, keeping it running, and other common questions.
Eco Purify Home System: specs and inclusions
Our three-stage whole-home filter: 5 micron pleated sediment, carbon and carbon block in 20 inch WaterMark housings, inside a weatherproof cabinet. Full specifications and what comes with it.
Changing the cartridges in a three-stage whole house water filter
A step-by-step for 20 inch three-stage systems: isolate the supply, release the pressure, replace the sediment, carbon and carbon block cartridges, reseat the O-rings, flush and check for leaks. Plus when to change them and how to read the gauge.
Care Plan: a new cartridge set every year, fitted or delivered
A single yearly charge once your included first year ends: cartridge set delivered, a reminder, fitting by our plumbers across Melbourne metro, and an extended warranty.
Common questions
Cartridge life, water pressure, installation, tank water, fluoride, pricing and the Care Plan.
Concerned about pressure at your home?
Send us your suburb and the number of bathrooms. We will let you know what your street supplies and how much of it the system will use.