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

Water purifier is located under the sink with no additional pumps, tanks or exposed parts. Innovative side loading design is convenient and does not require users to remove an entire system to replace filters.

Get fresh water conveniently

The fastest Reverse Osmosis RO water purifier to date, Max 4 produces a stream of clean water at 1800ml/min.

Faster flow rates mean instant clean water. Which in turn translates to a tankless, sleeker design that takes up less space.

Major size reduction from conventional RO filters

Advanced technologies allow the water purifier to produce water so quickly that they do not require a tank, saving space. The latest filter cartridges are smaller and more efficient.

Patented DIY Technology

Patent ZL 200910201739.8

Change your filters with two easy steps:

  1. Lift handle and pull filter out
  2. Push new filter in. An internal sensor calibrates your filter automatically.

Stage 1: MT-4, heavy duty pre-filter

A unique combination of four laboratory materials are designed to create a pre-filter which quickly removes impurities and most bacteria.

Stage 2: Patented CMF carbon filter

Patent ZL201520326026.5

Chlorides, which are prevalent in Singapore’s water supply are completely removed. Granulated carbon removes bad tastes, odors and all bacteria.

Stage 3: Patented Max 4 High precision RO filter

Patent ZL 200910201739.8

Traditional RO filters have water entering at one end and leaving at the other. These filters are the most expensive to replace and usually last a year.

Patented AOS RO filters are designed to allow water to stream in from both ends of the filter and bepurified through the length of the membrane. This design not only improves the filtration process, it also preserves the integrity of the filter, effectively extending its useful life to a remarkable 4 years.

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

Drinking water purifiers that filter with precision at 0.0001 microns.

Reverse Osmosis water filters

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

An RO filter is precise – up to 0.0001 microns. That’s three zeros. Most other water purifiers in Singapore only have the technology to filter up to 0.001 microns.

Singapore government uses Reverse Osmosis (RO)

PUB uses RO and ultraviolet (UV) to purify our water.

These are proven, internationally recognized 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