The mistake almost everyone makes is sizing off the number on the box. That number assumes a warm humid day, and your office will have plenty of days that are neither.

Step one: what your team actually drinks

Office water consumption is more predictable than people expect. A reasonable planning figure is 1 to 1.5 litres per person per working day across drinking water, tea and coffee.

Adjust upward if any of these apply: your office runs hot or has poor air conditioning; you have a lot of client meetings where water is served; there is a gym or people cycle in; or your team is heavy on tea and coffee. Adjust downward if many people bring their own bottles or work hybrid.

Step two: the mistake to avoid

Here is where sizing goes wrong. A 20L unit is rated at 20 litres per day — at 30°C and 80% relative humidity. An air-conditioned Johannesburg office in August is nowhere near those conditions.

Worse, air conditioning actively dehumidifies. The system that keeps your office comfortable is removing exactly the moisture your water generator is trying to collect. An AWG in a heavily air-conditioned space will underperform its rating even in summer.

So sizing off the rated figure means specifying a machine that meets your needs on the best day of the year and falls short on most others.

Step three: size against realistic output

Use the output curve rather than the headline number. For the 80L unit the manufacturer publishes tested figures at three conditions:

For a Johannesburg office, the middle row is the sensible planning assumption for much of the year, with the bottom row as your winter floor. That is why we would size one 80L unit to around 20–30 people rather than the 50+ its rating implies.

And this is exactly where purification mode earns its place in an office. On low-humidity days the machine runs from the mains supply instead, filters it through the same chain, and your team never notices the difference. In an office setting the dual mode is not a nice extra — it is what makes the sizing work year-round.

Rough sizing guide

Why bigger beats several smaller

If you need 80 litres a day, four 20L units and one 80L unit look equivalent on paper. They are not.

• Running cost. The 80L draws 1250W against 970W for the 20L, but produces four times the water. Per litre it is roughly a third of the cost.
• Maintenance. One set of filters on one schedule, versus four sets on four schedules.
• Purchase price. Four 20L units cost substantially more than one 80L unit for the same output.
• Floor space and sockets. Four machines need four places to stand and four outlets.

The case for multiple smaller units is genuinely about distribution, not capacity — if people would have to walk across the building, put a machine on each floor.

Placement in an office

• Away from the air-conditioning outflow. Do not put it where the AC is actively drying the air it is trying to use.
• Kitchen or break area, not a server room. Warmer and more humid is better, and that is also where people go for water.
• Give it airflow. Not boxed into a cupboard or shoved against a wall.
• Think about the walk. A machine people have to make a trip for gets used less than a water cooler in the kitchen — and then the bottled water creeps back in.
• Normal socket, no plumbing. Which means it can move if you rearrange, and it comes with you if the lease ends.

Comparing against what your office pays now

If you are on bottled water delivery, the comparison is not just cost per litre. Count the standing order somebody has to manage, the deliveries that arrive when reception is unattended, the empties stacking up, the storage space, and the weeks when your supplier cannot deliver because everyone else needs water too.

For a 20-person office getting through roughly 20 to 30 litres a day, the arithmetic tends to move decisively once you count the admin as a real cost — because somebody's time is being spent on it every month.

Related guides