PSI-021-4S 4 Stage Reverse Osmosis Under Sink Unit Standard Model

200 litre per day genuine Dow Filmtec membrane @50 psi, 300 litres @ 87 psi. LOW WASTE 1.25 to 1. All components are Australian Standards and or NSF certified. Optional ALKALIZER

Would you like to buy additional cartridges now?
Connection Fitting Option?
Faucet Standard Options?
Would you like to buy a hand held TDS meter now?
Optional re-mineraliser?
Tank size options?
Tax included


200 litre per day genuine Dow Filmtec membrane @50 psi, 300 litres @ 87 psi. LOW WASTE 1.25 to 1

All components are Australian Standards and or NSF certified & Watermarked

Optional with in-line re-mineraliser (ALKALIZER) making it a 5 stage extra $30.00

Replacement trio of cartridges (ROCDU-01) which is the annual change are $52.00

See faucet (tap) range, click here to viewFaucets.

Removes up to 98% of Fluoride, Substance treatment rates for TFC reverse osmosis, click here for a full list in PDF.

Click here to jump to the re-order for the correct annual trio pack of cartridges.

Click here to jump to the re-order for the correct membrane changed usually at the 4th year.

If your system has the in-line re-mineraliser/alkaliser fitted click here for that replacement cartridge, normally changed every second year.

1 Micron food grade polyspun sediment filter 9 ¾" (248mm) (standard size)

Omnipure OMB934-5M coconut carbon cartridge 9 ¾" (248mm) 37,000 litres chlorine rating

Genuine Omnipure CL10RO- high purity carbon post filter.

Genuine Dow Filmtec TFC Membrane (standard by which all other membranes are measured)

Main filter unit size, 42 cm high, 35 cm wide & 14 cm deep.

Supplied with a 350Kpa pressure limiting valve ( Watermarked and NSF Cerified).

9 litre stainless steel storage tank (exceeds drinking water guidelines) NSF Certified. If space is an issue we also offer a 4.2 litre or 12 litre tank.

Click here for tank details.

Standard type flow restrictor

Installation choice 1/2" tee olive fitting, 3/4" dishwasher adapter or 1/2" easy fit braided line flick mixer adapter, our systems take the average handyman 1/2 to 1 hour to install

Mains connect systems

Click here to view how each are installed water filter parts

This Reverse Osmosis system was originally developed to compete directly with the Chinese imported systems.

At first we tried the same components as they use but with better Taiwanese housings and American cartridges, but some of the components during testing failed.

First we up-graded the auto shut off valve to the U.S.A. made Hydromatic valve which has proved to be very reliable as well as the Hydromatic check valve, we then found the Chinese copy of the Jaco fittings to also be of poor quality and subject to blow off so we up-graded them to the genuine Jaco gripper series which never let go, then it was the tubing that we up-graded to the genuine British John Guest tubing which is extremely high quality, next was the Faucet, we purchased some of the non NSF faucets to supply with the system but with between 6 to 11% lead content in the brass the faucet was made from the water had a metallic taste when first used after sitting say overnight so we tossed those faucets in the garbage and purchased NSF no lead faucets to supply with the systems, so in the end we found that we had a system that was reliable but costs more to produce than the Chinese systems.

The PSI-021-4S may not be as cheap as the Chinese systems but we could not sell a system that would have been a problem for our customers as well as being a warranty nightmare for us.

In the end the PSI-021-4S Undersink reverse osmosis system is good quality, is reliable, suits those looking for a budget system without running the risk of buying a system that will give them problems, the price doesn’t match the Chinese systems but we would rather miss a sale than sell something that would fail. product comes complete, ready for installation.

All reverse osmosis systems require a minimum pressure of 40 psi (280kpa) with 50 psi (350kpa) or more is ideal. If you are unsure what your pressure is check with your local Council or water authority.

Substance treatment rates for TFC reverse osmosis, click here for a full list in PDF.

If you choose to have the TDS meter with the unit beware that the system will have an elevated reading due to having the reminerliser cartridge.

Product Details

Data sheet

3 Years Warranty
5 other products in the same category:

QR04 Premium Reverse Osmosis


The QRO4 are often also sold under the names HydrROtwist or PuRO Twist. The QRO4 that we stock have the faster 50 gallon per day (200 litre) membrane compared to others which have slower membranes. These are so easy to change the cartridges on that

Price $663.00
In stock

PSI 021-Alka


PSI 021-Alka- Introducing our newest model to our ever increasing range of reverse osmosis systems. This system has been designed with the latest technology of the PI filters. Assembled here in Australia with quality components from countries like America.

Price $556.75 Regular price $655.00
In stock
chat Comments (0)
No customer reviews for the moment.
Customers who bought this product also bought:



This whole house system, first stage uses a 20 Inch big blue housing with a 1, 5, 10 or 20 micron polyspun sediment filter and the second stage uses a 20 Inch big blue housing with a Coconut 20 Inch x 4.5 Inch extruded carbon cartridge.

Price $450.00
In stock

Follow us on Facebook