Buy DI-only if your tap water reads under 50 ppm; buy RO+DI if it reads over 100 ppm or you clean more than once a week. DI resin gives instant 0 ppm water but exhausts by volume; an RO membrane removes 95–98% of minerals first, so the resin only polishes and lasts many times longer.
The two ways to make pure water
Reverse osmosis forces water through a membrane that rejects dissolved solids. It is slow, rated in litres per day, and sends a waste stream to drain — but its running cost is minimal. Deionisation swaps ions chemically in a resin bed. It is instant and portable — but the resin is a consumable you replace.
Head to head
| DI-only | RO + DI | |
|---|---|---|
| Upfront cost | lowest | from R3,900 extra |
| Cost per litre | rises with tap TDS | near zero after purchase |
| Output speed | instant, full flow | rated (264 GPD ≈ 1,000 L/day) |
| Waste water | none | brine stream to drain |
| Best for | low-TDS areas, occasional use | weekly work, inland water, teams |
Decide with a meter, not a guess
Measure your actual tap water with a TDS meter before spending anything. Under 50 ppm, resin lasts long enough that DI-only wins on simplicity. Between 50 and 100 ppm, usage frequency decides. Over 100 ppm — common inland — resin-only becomes the most expensive water you can make, litre for litre. The consumable maths is broken down in the DI resin guide.
The setup professionals converge on
Most full-time cleaners end at the same architecture: RO membrane doing 95–98% of the work, small DI vessel polishing to 000, meter confirming the output. It is the configuration with the lowest cost per clean and the one our waterfed pole equipment guide recommends as standard.
The hardware
Static setup: the reverse osmosis system (R3,900) feeding your vessel. Fully mobile: the RO water trolley (R15,210) — filtration on wheels for site work. Complete pole-and-water packages are under waterfed pole systems.