A. O. Smith Drinking Water Filter

Max 4 Water Filter*

0.0001 micron Reverse Osmosis water purifier, with refill cartridges designed to be easily replaced on your own. 

*may be paired with an AOS hot water tap

Fully integrated system

The Max 4 water purifier is located under the sink with no additional pumps, tanks or exposed parts.

Its innovative side loading design is convenient and does not require users to remove an entire system to replace filters.

Get fresh water in seconds

With the latest RO water filter technology, Max 4 produces a jet of instant, clean water at 1800ml/min. Conventional RO filters operate at 200ml/min.

Tankless and space saving

Producing clean water 9 times faster eliminates the need for a tank. While conventional RO filters are bulky, the Max 4 is a tankless, sleek design that takes up less space in your kitchen.

Patented DIY Technology

Patent ZL 200910201739.8


Change your filters in two easy steps:

Step 1:
Lift handle and pull filter out

Step 2:
Push new filter in. 


Each filter is fitted with a mircochip that records your volume consumption and life of the individual filter. Change only the filters which are depleted. 


Stage 1: Heavy duty sediment pre filter

In the first stage, a heavy duty pre filter clears out impurities and sediments from the water. This prolongs the life of the stage 2 and 3 filters. Sediment filters operate efficiently for up to a year.

Stage 2: Patented carbon chlorine filter

Patent ZL201520326026.5

Patented carbon filter intercepts and removes an extremely high rate of 99.9% of bacteria and chlorides. Odours are eliminated and water taste improves significantly.

Stage 3: Patented high precision RO filter

Patent ZL 200910201739.8


Traditional RO filters have water entering at one end and leaving at the other. These high pressure RO systems usually last no more than a year. 

The Max 4 high precision filters can last up to 4 years. They are designed to allow water to stream in from both ends of the filter and be purified through the length of the membrane. This design not only preserves the integrity of the filter for longer, it also improves the entire filtration process.

AOS RO Technology: Highest water retention rate

To obtain the cleanest water, all RO water purifiers can retain only a percentage of the water. The more advanced the RO filter, the higher the retention rate.

While other RO water purifiers have a water retention rate of 25%, the AOS RO filter holds the patent for the highest water retention rate of 75%.

Dual filter replacement indicator

Light indicator at both hot water faucet and water purifier changes colour to reflect life of the filter, giving you ample time to arrange for filter replacements.

White – Normal
Orange – 5% life
Red – 0% life

Automated self-cleaning

Max 4 auto-cleanser performs a flush through the entire system. It is activated:

  • upon powering up or after a reset
  • for every 30 min of continuous usage
  • for every 72 hours of inactivity

100% fully-owned robotic plants

To maintain high quality control, A. O. Smith Corporation fully owns every of their 21 plants worldwide. They are the only manufacturer with the technology to employ robotics over 95% of their production line.

Established in 1874

A. O. Smith Corporation has led the industry in the development of advanced automated technology, manufacturing car frames for Ford and Cadillac in the 1900s. The consistency of their processes have been unparalleled in the last 100 years.

AOS Water Filters

High Precision RO drinking water purifier. Tank size suitable for families of 4. 

Reverse Osmosis water filters

AOS water purifiers use Reverse Osmosis (RO), the top international standard for clean drinking water

RO filters use high precision filtering up to 0.0001 microns.
Most water purifiers in Singapore filter up to 0.001 microns.

PUB uses Reverse Osmosis (RO)

PUB uses RO and ultraviolet (UV) to purify our water.
These are proven, top in range methods for purification.

RO Water – #1 in USA and China

In places where water purification is essential, RO is always used as 0.0001µ filtration ensures that all trace heavy metals are removed.

RO is the top water purification system used in USA and China.

Filter replacement indicator

Light indicator at drinking water tap changes colour to reflect life of the individual filters, giving you ample time to arrange for filter replacements.

White/Green– Normal
Orange– 5% life
Red– 0% life


under-sink installation
Model Max 4 AR-75
RO filter 0.0001 micrometers

Rated volume produced 7500 liters 5000 liters
Maintenance DIY
Filter 1 (1 year) $80
Filter 2 (1 year) $70
Filter 3 (4 years) $250
Size (mm) 140 (W) x 430 (H) x 445 (D) 260 (W) x 420 (H) x 410 (D)
Power (W) 107 25
Voltage, Hz 220V, 50-60Hz 220V, 50-60Hz
Filtration rate 1800 ml/min 196 ml/min
Water supply pressure (MPa) 0.10 – 0.35 0.10 – 0.35
Weight (kg) 15.5 11.0
Warranty 1 year 1 year