A useful RO enquiry begins with a representative feed-water sample and a report that an engineer can interpret. TDS by itself cannot show which salts may concentrate, what pretreatment may be needed or whether the sample represents the intended operating season. Use this checklist to assemble screening information; the final test scope still depends on the source and product-water use.
1. Make the sample traceable
Record the source, exact sampling point, collection date and time, and whether the sample is raw water or water after an existing treatment step. Add temperature, recent weather or production events, seasonal high and low conditions, and any blending ratio. A composite from unidentified points can hide the condition that governs design, so keep sources separate unless the planned plant will blend them at a controlled ratio.
Ask the laboratory to state units, analytical methods, detection limits and preservation conditions. Field measurements such as temperature, pH, conductivity, turbidity and disinfectant residual should be taken close to sampling when practical. List every chemical already added upstream, including coagulant, oxidant, reducing agent, softener regenerant or pH modifier. This context lets the reviewer distinguish the natural source from treated feed conditions.
2. Provide the ionic matrix, not TDS alone
Include major cations and anions with a consistent reporting basis: calcium, magnesium, sodium, potassium, bicarbonate or alkalinity, sulfate, chloride, nitrate and fluoride. Add silica, barium, strontium, iron, manganese and aluminum where relevant, distinguishing total and dissolved results when the laboratory provides both. Phosphate, boron and other source-specific constituents may be needed when the source or intended product makes them material.
A reviewer uses the ion set and pH to check electrical balance, carbonate chemistry, osmotic conditions and possible mineral saturation as concentration rises through the RO train. The EPA model documentation, for example, balances anions and cations and evaluates carbonate, silica, calcium sulfate and calcium fluoride conditions. This does not create a universal acceptance limit; it shows why a single conductivity or TDS number is not an adequate design basis.
3. Describe fouling risks and the required product
Report turbidity and suspended solids, and provide SDI when a representative pretreated RO feed can be tested. Depending on the source, add TOC or COD, oil and grease, microbiological indicators, sulfide, residual chlorine and other oxidants. Industrial reuse water often needs a different panel from stable groundwater. State known upsets, cleaning chemicals, process carryover and the worst credible seasonal condition instead of submitting only the best recent result.
Finish the enquiry with required permeate flow, operating hours, intended use and numerical product-water limits at the agreed verification point. Include available feed pressure, temperature range, discharge route for concentrate and site utility constraints. The supplier can then define any further sampling, projection and pilot work before selecting pretreatment, recovery, membrane arrangement or guarantees. This checklist supports preliminary engineering; it does not replace a project-specific design review.
Data to collect before comparing proposals
| Parameter / interface | Unit / format | Why it matters |
|---|---|---|
| Sample identity | Source, point, date, season | Keep raw and pretreated samples clearly separated. |
| Field condition | Temperature, pH, conductivity, turbidity | Record promptly and note unusual operating events. |
| Major cations | Ca, Mg, Na, K | Use consistent units and laboratory methods. |
| Major anions | Alkalinity/HCO3, SO4, Cl, NO3, F | Provide enough data for an ionic-balance review. |
| Scaling species | Silica, Ba, Sr and source-specific ions | Do not infer scaling risk from TDS alone. |
| Metals | Fe, Mn, Al; total/dissolved if available | Identify upstream chemicals and existing treatment. |
| Fouling indicators | SDI, solids, TOC/COD, oil or biology as relevant | Tailor the panel to groundwater, surface water or reuse. |
| Oxidants and reducers | Free/total chlorine, sulfide or relevant residuals | State dosing points and sample timing. |
| Product and duty | Permeate limits, flow and operating hours | Define the use and the verification location. |
Technical references
- DuPont FilmTec — Reverse Osmosis and Nanofiltration Technical Manual ↗Source checked:
Evidence scope — original English record
Reference list for RO water analysis and operating records, including ionic species, silica, conductivity, pH, TOC, SDI or turbidity, temperature and residual chlorine.
- US EPA — WBS Cost Model for Reverse Osmosis/Nanofiltration Drinking Water Treatment ↗Source checked:
Evidence scope — original English record
Engineering model documentation showing the use of feed-water ions, pH, charge balance, scaling indices, SDI, pretreatment assumptions and design targets.
- BOKAWATER — Container RO product reference ↗Source checked:
Evidence scope — original English record
Existing BOKAWATER RO product-family reference only; this checklist does not select a model or assert project performance.