RO vs DI Window Cleaning Systems
Both RO and DI systems can produce pure water for spotless window cleaning, but they work differently. Choosing the right setup can save money, reduce resin use and make your window cleaning system more efficient.
Quick Answer
DI-only systems are simple, compact and good for soft-water areas or lower water use. RO/DI systems are usually better for professional window cleaners using larger volumes of water, especially in medium or hard-water areas.
What does pure water mean?
Pure water is water that has had dissolved minerals removed. These minerals are measured as TDS, which stands for Total Dissolved Solids. When ordinary tap water dries on glass, minerals can be left behind as spotting or streaking.
For window cleaning, the aim is normally to produce water at or very close to 0 TDS. Once the water is pure, it can dry naturally on the glass without leaving mineral marks behind.
What is DI filtration?
DI stands for deionisation. A DI system uses a vessel filled with mixed-bed resin. As water passes through the resin, the resin removes dissolved ions from the water.
DI systems are popular because they are simple. There are no membranes, waste water lines or complex setup requirements. For small setups or cleaners in soft-water areas, DI-only can be a very practical option.
DI is best suited to:
- Soft-water areas
- Small trolley systems
- Occasional pure water use
- Lower daily water production
- Final polishing after RO filtration
The downside is running cost. In harder water areas, the resin has to do all the work. That means the resin exhausts faster and needs replacing more often.
What is RO filtration?
RO stands for reverse osmosis. An RO system pushes water through a membrane that removes most of the dissolved solids before the water reaches the DI resin.
A typical professional RO/DI setup includes pre-filters, an RO membrane and a DI vessel for final polishing. The RO membrane does the heavy lifting, while the DI resin finishes the water down to 0 TDS.
RO/DI is best suited to:
- Medium and hard-water areas
- Daily professional window cleaning
- Van-mounted systems
- Large storage tanks
- High water usage
- Single or multi-operator setups
RO vs DI: which is better?
| Setup | Advantages | Best For |
|---|---|---|
| DI Only | Simple, compact, lower upfront cost, easy to maintain. | Soft-water areas, lower water use, small trolley systems. |
| RO/DI | Lower resin use, better for hard water, better for high-volume production. | Professional van systems, daily users, larger tanks, hard-water areas. |
Why water hardness matters
Your incoming tap water makes a huge difference. A cleaner in a soft-water area may be able to run DI-only without high resin costs. A cleaner in a hard-water area may burn through resin very quickly if they rely on DI alone.
This is why the first step is always to test your water with a TDS meter. Once you know your incoming TDS, you can make a sensible decision instead of guessing.
Simple rule
If your water is soft and your usage is low, DI-only may be enough. If your water is medium to hard, or you are filling a van tank every day, RO/DI is normally the better long-term setup.
Running costs: resin vs membrane
DI resin is a consumable. The harder your water and the more water you use, the faster it gets used up.
An RO system costs more to set up, but it reduces the amount of work the DI resin has to do. For professional window cleaners producing hundreds of litres per day, this can make RO/DI much cheaper to run over time.
Where does hot water fit in?
RO and DI are about water quality. They help produce pure water that dries spot-free.
Hot water is about cleaning performance. Heated water can help on first cleans, greasy frames, bird mess, winter work and stubborn dirt. That is where systems such as the Pure Heat range can complement a pure water setup.
Put simply: pure water gives the spotless rinse. Hot water helps shift the dirt.
Which system should you choose?
Choose DI-only if:
- You are in a soft-water area
- You use relatively small amounts of water
- You want a simple starter setup
- You are running a trolley or compact system
Choose RO/DI if:
- You are in a medium or hard-water area
- You fill a van tank regularly
- You clean windows professionally every day
- You want to reduce resin running costs
- You are building a larger or multi-operator setup
Common questions
Can DI resin produce 0 TDS water on its own?
Yes. DI resin can produce 0 TDS water, but how long it lasts depends heavily on your incoming tap water and how much water you produce.
Does RO water still need DI resin?
Usually, yes. RO removes most dissolved solids, but DI resin is normally used after the RO membrane to polish the water down to 0 TDS.
Is RO always better than DI?
No. RO/DI is usually better for higher water usage and harder water areas. DI-only can still be a good option where water is soft or usage is low.
What TDS should window cleaning water be?
Most professional window cleaners aim for 0 TDS for spot-free results.
Related guides
Need help choosing the right pure water setup?
Speak to Precious Washers for advice on RO systems, DI resin, TDS meters, tanks, reels, Pure Heat hot water systems and complete window cleaning van setups.
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