Everyone asks about the purchase price. Almost nobody asks what it costs to fill a glass, which is the number that actually decides whether this makes sense for you.

The tariff you are actually paying

City Power's residential prepaid tariffs, effective 1 July 2026 and including VAT, run in blocks:

Here is the part people get wrong. An atmospheric water generator is additional load on top of everything you already use. So it is not billed at your average rate — it is billed at your marginal rate, the top block your household reaches. For most Johannesburg homes running a fridge, geyser and the usual appliances, that is Block 3 at R4.37/kWh.

Calculating with your average rate will make the machine look about 25% cheaper to run than it is. We are using the marginal rate throughout, because that is what actually lands on your bill.

The arithmetic

Two numbers drive everything: rated power draw, and how many litres the machine produces while drawing it.

A compressor cycles rather than running continuously, so actual consumption depends on duty cycle — the share of the day the compressor is actually working. To hit rated output on a warm humid day, expect it to run most of the time. We have shown the full range so you can place your own situation on it.

SkyTap 20L, at R4.37/kWh

SkyTap 80L, at R4.37/kWh

Two things that table tells you

First: bigger is dramatically cheaper per litre. The 80L unit draws only 29% more power than the 20L but produces four times the water. At rated conditions that works out to roughly R1.64 per litre against R5.09 — about a third of the cost. If you are choosing between several small units and one big one for the same total output, the big one wins on running cost by a wide margin, before you even compare purchase prices.

Second: dry weather is where the cost lives. That R11.92 figure in the bottom row is not a typo. The machine draws the same power regardless of humidity — what changes is how much water it gets for that power. At 30% relative humidity you are paying roughly seven times more per litre than at 80%.

This is the single most important thing to understand about running one of these, and it is why the purification mode matters so much in practice. On a dry August day you are far better off feeding the machine tap water and letting it purify, than running it in atmospheric mode at twelve rand a litre.

How this compares to what you are paying now

Context makes the numbers meaningful. Bottled water in South African retail typically works out somewhere around R5 to R8 per litre for 5L containers, before you count the trip to fetch them. Office water delivery lands in a similar range once the service fee is included.

So an 80L unit at rated conditions produces water at roughly a quarter to a third of bottled water cost. A 20L unit at full duty produces water at roughly the same cost as bottled. The machine's advantage in that case is not the price per litre — it is that the water is there without a delivery, a standing order or a shop run.

What else it costs

Electricity is the main ongoing cost but not the only one. Filters are consumables and need replacing on a cycle — that is a real cost to budget for, whether you buy them yourself or take a maintenance plan. Beyond that there is very little: no plumbing, no water bill for what it generates from the air, and no delivery fees.

Reducing your running cost

• Run it where the air is warmest and most humid. A kitchen generally beats an air-conditioned office, because air conditioning actively removes the moisture your machine is trying to collect.
• Switch to purification mode when humidity drops. Below roughly 40% relative humidity, the cost per litre in atmospheric mode climbs steeply. Filtering tap water uses a fraction of the energy.
• Do not put it in a sealed, dry room. The machine needs airflow. Starving it of fresh humid air means it works longer for less.
• If you have solar, run it during the day. This is a daytime-friendly load and it pairs unusually well with a PV system.

Working out your own number

Use this and substitute your own tariff:

The variable that moves the answer most is not your tariff — it is the litres in the denominator, which is set by your humidity. Anyone quoting you a fixed cost per litre without asking where you live is guessing.

Sources. Tariffs from EnergyBee — City Power July 2026 tariff breakdown, effective 1 July 2026, VAT inclusive. Power draw and output figures are the manufacturer's rated specifications for the units SkyTap supplies. Duty-cycle scenarios are modelled ranges, not measured values — your actual consumption will depend on your environment.

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