Short answer: Reverse-osmosis water can be too low in conductivity for some combi-oven controls unless it is remixed or configured correctly. ‘Purer’ is not automatically more compatible.
An RO system removes scale risk but the appliance develops sensing or filling problems. The common misconception is that the lower the mineral content, the safer the water for every steam appliance. This article turns that assumption into specific checks that can be recorded on the drawing, survey or commissioning sheet.
Model-specific rule: Water limits differ by model; use laboratory/site test results and manufacturer approval where required. Where gas, electricity, refrigeration, guarded components, hot oil, pressure or safety controls are involved, use the appropriately competent engineer and never bypass a safety device.
Conductivity can be an operating requirement
Some level-detection and water systems rely on a minimum conductivity range. Very low-mineral water can therefore create fill or sensing behaviour even though scale risk is reduced.
- Measure conductivity after treatment.
- Compare with the exact model limit.
- Check whether remix/bypass is required.
RO does not solve every chemistry risk
Membrane performance, chlorides, pH and maintenance affect the final water. A system specified only as ‘RO’ does not prove what reaches the appliance.
- Test the delivered water, not the label.
- Record membrane and cartridge condition.
- Check each appliance inlet separately.
Treatment is part of commissioning
The treatment system should be set under realistic flow, then rechecked. A sample taken from a stagnant branch may not represent operating water.
- Flush before sampling.
- Record flow and sample point.
- Retain results with the appliance documents.
What the site evidence may show
| Observation | Hidden issue | Next check |
|---|---|---|
| RO unit is installed | Conductivity is below limit | Assess approved remix/configuration |
| Scale is reduced | Corrosion chemistry is unchecked | Test full water specification |
| Commission sample passes | Service drift changes output | Plan periodic testing/maintenance |
A practical verification sequence
- Confirm the exact duty and model. Record what the appliance or space must achieve at peak service and use the current model-specific installation information.
- Draw the complete interface. Include moving parts, service/removal access, connections, adjacent equipment and the real operator or trolley position.
- Measure under a representative condition. Static, empty or isolated tests can hide the issue. Record the operating state, value, unit and test point.
- Correct and prove. Repeat the same test after any change and retain the evidence with commissioning or O&M information.
Checks to record:
- Conductivity.
- hardness.
- chlorides.
- pH.
- temperature.
- treatment configuration.
- inlet-specific requirements..
Explain conductivity thresholds, remix/bypass options, chlorides and why treatment must meet the exact manufacturer envelope rather than a generic ‘RO’ label. The result should be a measurable decision rather than a generic note such as “allow sufficient space” or “services by others”.
Common mistakes to avoid
- Assuming zero hardness is the whole requirement.
- Quoting raw-water results for treated water.
- Changing remix settings without manufacturer/treatment advice.
- Failing to test after cartridge or membrane changes.
Frequently asked questions
Does every combi oven have a minimum conductivity?
No. Check the exact model; requirements and sensing methods differ.
Can softened water and RO be treated as the same?
No. They change water chemistry in different ways and must be selected against the appliance limits.
What records should be kept?
Raw and treated test results, treatment settings, sample point, date, flow condition and maintenance schedule.
Related Kitchen Install Guide reading
- How Low Water Pressure Causes Dishwasher and Combi-Oven Faults
- How Water Treatment Problems Damage Kitchen Equipment
- Commercial Kitchen Equipment Commissioning Documents
Record the installation detail before handover
Use the KIG 318 Commercial Kitchen Installation Checklist to record equipment interfaces, measured conditions, outstanding actions and acceptance evidence.
Sources and further guidance
Last reviewed: 14 August 2026. This article provides general commercial-kitchen design and installation information. It does not replace the exact manufacturer instructions, a site-specific design, risk assessment or work by competent specialists. Stop use and obtain competent help where equipment or services may be unsafe.