How to Write an RO Procurement Spec That Gets You Comparable Quotes (and the One Most Buyers Forget)
By Ella Liu — Industrial Water Treatment Specialist at Rong Water. 10+ years sizing RO, UF, deionised, EDI ultrapure and GMP purified water systems.
You sent an RFQ to three RO vendors. Two weeks later you have three quotes that look the same on the cover page and are completely different underneath. One quotes 24 elements at 18% recovery; one quotes 30 elements at 22% recovery; one quotes a single-pass system with no second pass. The numbers in column “capacity” all say 100 m³/h, but none of them will deliver the same water at the same OPEX.
None of that happened because one vendor is dishonest. It happened because the procurement spec let each vendor fill in the blanks differently — different assumptions about flux, recovery, target permeate quality, and what counts as a “membrane”. Three technically valid quotations you cannot fairly compare.
This article is the 10 lines you need in a spec to force all vendors onto the same basis, plus the one clause (membrane warranty) that decides who eats the risk if the membranes fail early. If you have not sized the system yet, read How to Size an Industrial RO System first — this article assumes you have a target flow and quality, and you are now buying the equipment.
Why most RO RFQs are uncomparable
Three patterns repeat in RO bids that go wrong:
1. The capacity is stated but the recovery is not. Vendor A quotes 100 m³/h permeate at 75% recovery; vendor B quotes the same permeate at 70%. A and B have the same product flow on paper but a 5% difference in feed flow — and a different element count. To compare them, you must convert each quote back to feed flow and energy per cubic metre of permeate.
2. The “membrane” is generic. Vendor A quotes “Dow FilmTec equivalent”; vendor B quotes “LG equivalent”; vendor C quotes an unbranded element. These have very different flux ratings, salt rejection and service lives. Without a named membrane on every quote, the bids are not the same equipment.
3. The acceptance criteria are vague. “System shall produce 100 m³/h permeate” — at what temperature, at what recovery, at what feed TDS, with what salt passage? The same system can hit that target at 25 °C and miss it at 15 °C. Without performance gates, the vendor can claim nominal compliance on a quote that fails in real operation.
Ten mandatory spec lines fix it. Vendors who can’t quote to them are out; vendors who can are compared like-for-like.
The 10 spec lines that make quotes comparable
Line 1: Feed water analysis (mandatory)
Without real data, every vendor quotes on an assumed feed — and they’ll assume the worst case they’ve seen. The minimum set:
- TDS (or conductivity)
- Hardness (Ca²⁺, Mg²⁺ as CaCO₃)
- Alkalinity (M-alkalinity, P-alkalinity)
- Free chlorine / total oxidants
- Iron, manganese
- Sulfate, chloride, silica
- pH
- Temperature range (winter/summer)
- SDI (or silt density index)
- TOC, COD
No full lab analysis? Send what you have plus the source — municipal, well, surface, or seawater. It beats silence every time.
One mistake I keep seeing: the spec says “Feed is city water.” City water in Shanghai is not city water in Cairo. Pin the analysis, or accept that the vendor will assume the worst case they’ve seen and price it.
Line 2: Permeate flow, normalised
Specify permeate flow at design temperature, with an explicit normalisation reference (typically 25 °C). Without this, a vendor can quote the same flow at a winter temperature they will not actually achieve.
| Field | Example |
|---|---|
| Permeate flow | 100 m³/h |
| Reference temperature | 25 °C |
| Recovery | 75% |
| Permeate TDS target | < 500 mg/L (or < 50 mg/L for high-purity duty) |
The normalisation is the single most important clause. If you skip it, the bid cannot be evaluated on water cost.
Line 3: Recovery, single number
Pin recovery to one value. “75% nominal, acceptable range 70–80%” is a stronger spec than “high recovery” because vendors cannot each pick a different number.
For seawater RO, the recovery band is much narrower (35–45%); for high-purity industrial water (boiler feed, electronics) it can be 80–90% in two-pass configurations. State the band; let the vendor choose the operating point inside it.
Line 4: Feed pressure and concentrate pressure
Specify the maximum feed pressure at design flow. Without this, a low-pressure design (more elements, more pumps) can match a high-pressure design on permeate flow while costing more to operate.
- Standard brackish RO: ≤ 1.0 MPa at design flow
- High-recovery / high-TDS brackish: ≤ 1.5 MPa
- Seawater RO: ≤ 6.0 MPa (with energy recovery)
The pressure ceiling forces vendors to optimise element count and pump selection instead of adding elements to lower pump cost.
Line 5: Named membrane, with quantity
Do not accept “8-inch RO membrane” or “equivalent to Dow FilmTec”. Specify:
- Manufacturer (LG, Toray, DuPont, Vontron, or named equal)
- Model number (e.g. LG BW400-UD, DuPont BW30-400)
- Quantity per train
- Element count per pressure vessel
- Vessel count per train
Name the membrane and this bid stops being opaque. Two vendors quoting the same flow at different element counts are quoting different flux — and the lower-flux quote will have a longer membrane life. That’s exactly the difference you want to see on the page.
Line 6: Skid, frame and instrumentation scope
Specify whether the bid is for:
- Equipment only (skid, vessels, pumps, instruments)
- Equipment + controls (PLC, HMI, SCADA)
- Equipment + controls + installation (piping, electrical, civil interface)
- Turnkey (everything including commissioning)
Leave this open and vendor A quotes just the vessels and pumps, vendor B quotes a complete packaged plant, vendor C quotes equipment plus installation. The column marked “price” now covers three different scopes — and buyers compare them on raw number all the time. A “cheaper” equipment-only quote can end up more expensive than the turnkey once you add your own installation and commissioning.
For food and beverage plants and pharmaceutical purified water projects, hygiene-grade skid scope (SS316L piping, sanitary fittings, electropolish) is non-negotiable — a stainless-steel-304 quote from a vendor without pharma experience will fail FAT. For power station boiler makeup and seawater desalination duty, high-pressure vessel rating and corrosion-resistant frame materials matter most. The scope must match the duty.
Line 7: Energy and chemical consumption at design
Two quotes can match on capex and differ by an order of magnitude on OPEX. Force the vendors to state, at design flow and design recovery:
- Specific energy consumption (kWh per m³ permeate)
- Antiscalant consumption (mg/L feed)
- CIP chemical consumption (per cleaning, per year)
- Membrane replacement schedule and cost (over 5 years)
The OPEX line is the one buyers most often skip — and the one where 5-year total cost differs by 30% between competitive bids.
Line 8: Performance acceptance test protocol
State how the system will be accepted:
- Test duration (typically 7–14 days of continuous operation at design)
- Performance gates (permeate flow, permeate TDS, salt passage, recovery, energy consumption)
- Permissible deviation (e.g. ±5% on flow, ±10% on salt passage)
- Conditions under which the test is run (feed water, temperature, recovery)
A vague acceptance test (“system shall meet design parameters”) gives the vendor no accountability. A specific test with gates gives you leverage to require the vendor to fix what does not meet spec.
Line 9: Membrane warranty and pro-rata terms
If you skip one line on this whole template, don’t skip this one. The membrane warranty decides who eats the cost when membranes fail early — and it’s the line I see left blank in more RFQs than any other.
Standard membrane warranties are 3 years pro-rata — the vendor pays a declining share of replacement cost based on months of service. Stronger terms (5 years full replacement in year 1, then pro-rata) are available from premium vendors; weaker terms (1 year) are common from low-end vendors.
The warranty is particularly important when the RO train feeds a downstream EDI ultrapure stack or a purified water GMP system — membrane failure cascades into the polishing stage and shuts down the entire pharmaceutical water or power boiler line. The economic loss from a 5-day outage is often larger than the membrane replacement itself, so warranty strength matters more than capex.
| Warranty format | What it means for you |
|---|---|
| 3-year pro-rata from month 0 | Vendor pays 100% in month 0–12, declining linearly to 0 in month 36 |
| 3-year, year-1 full + years 2–3 pro-rata | Strong — covers early failures completely |
| 1-year full, no further warranty | Weak — you pay for everything after month 12 |
| No warranty specified | Disqualifying — never accept |
Specify warranty in months and pro-rata curve, and require named-coverage in the vendor’s quotation. Without it, two bids at the same price are not the same risk.
Line 10: Documentation, training and spares
For a 100 m³/h industrial RO train, the minimum documentation scope is:
- P&ID (piping and instrumentation diagram)
- GA drawings (general arrangement)
- Electrical schematics and PLC program
- O&M manual with CIP recipes (see B1: RO Membrane CIP)
- Commissioning record
- Spare parts list (recommended stock for 2 years of operation)
Specify whether training is included (typically 2–5 days on-site for operators), and whether the bid includes a recommended spares package. A bid without documentation and training is incomplete even if the equipment is cheaper.
The clause most buyers leave out: the acceptance holdback
Beyond the 10 spec lines, one clause turns a procurement spec into risk protection: the acceptance holdback.
A typical clause: “10% of the contract price is withheld until the performance acceptance test is passed, with all gates met, within 90 days of delivery.”
This does three things:
- Gives the vendor an incentive to commission properly. Many plants are delivered, started up partially, and abandoned on the vendor’s part once payment clears. A holdback keeps them on the hook.
- Forces a real performance test. Without a holdback, the vendor can argue performance is a “site issue” indefinitely.
- Aligns the vendor with your operating team. They need your operators trained and the system stable before they get paid — so they will help you get there.
A 10% holdback is industry standard. Watch how a vendor reacts to it — that reaction tells you more than their brochure.
Putting the spec together: a 10-line template
A complete RO procurement spec for a 100 m³/h industrial water plant can be summarised in 10 lines. Vendors quote against these 10 lines; bids are compared line-by-line.
1. Feed water analysis (TDS, hardness, alkalinity, Cl2, Fe, Mn, SO4, Cl, SiO2, pH, T-range, SDI, TOC)
2. Permeate flow 100 m³/h normalised to 25 °C, recovery 75% nominal (band 70–80%)
3. Permeate TDS < 500 mg/L, salt passage < 1%
4. Feed pressure ≤ 1.0 MPa at design
5. Membrane: LG BW400-UD (or named equal), 27 elements in 9 vessels × 3 trains
6. Scope: skid + vessels + pumps + instruments + controls (PLC/HMI) + commissioning
7. OPEX: SEC ≤ 0.75 kWh/m³ permeate, antiscalant ≤ 5 mg/L feed, CIP ≤ 4×/year
8. Acceptance test: 14-day continuous, ±5% on flow, ±10% on salt passage
9. Membrane warranty: 3-year pro-rata, year-1 full coverage
10. Documentation: P&ID, GA, electrical, PLC program, O&M manual, 3-day operator training
11. Holdback: 10% of contract price, released on acceptance test pass
Eleven lines, three pages maximum. Send this to three vendors; you will get three comparable bids.
What to look for in the vendor’s response
Once the bids come back, evaluate line by line:
| Evaluation point | What to compare |
|---|---|
| Element count and configuration | All bids should quote the same named membrane at similar flux |
| Pump manufacturer and model | CNP, Grundfos, DAB — comparable cost tiers; reject no-name pumps |
| Vessel pressure rating | 150 psi (10 bar) standard for brackish; 300 psi (20 bar) for high-pressure |
| Frame material | SS304 minimum, SS316L for high-purity duties (food, pharma) |
| Controls platform | Siemens / Allen-Bradley / Schneider — established vendors with spares support |
| Instrumentation brand | Endress+Hauser, Siemens, Yokogawa — same tier across bids |
| Warranty in months and pro-rata | Reject any bid that does not name both |
| Lead time | Realistic 8–14 weeks for a 100 m³/h industrial train; longer means overseas sourcing |
Reject bids that quote a different membrane than specified without an equivalent. Reject bids that omit OPEX lines, warranty terms, or acceptance gates. These omissions are where post-purchase disputes live.
For our standard packaged RO configuration that meets this template, see the RO-4000 industrial reverse osmosis system. For smaller industrial duties where a UF-2000 skid feeds the RO train, the same procurement principles apply with different scope weighting. For lower-purity industrial deionised water duty where DI-1000 replaces a separate EDI polishing stage, the spec needs to reflect the integrated scope.
After the spec: what to expect from a competent vendor
Watch what the vendor does next. A competent one will come back with questions before bidding — about how complete the feed analysis is, the electrical supply, the building footprint, the existing pretreatment, the operator skill level, the export paperwork. A vendor who takes those details seriously is a vendor who wants the project to work.
A vendor who quotes straight to your 10 lines without asking a single question is either guessing or forcing a standard package to fit. You’ll find out which one in the first month of operation.
For the system design these specs buy, see How to Size an Industrial RO System. For the polishing stage typically following it, see EDI vs Mixed-Bed Polisher. For the cleaning regime that keeps the membrane operating at design, see RO Membrane CIP: When to Clean, When to Replace.
FAQ
What is the most common mistake in an RO procurement spec?
Accepting “RO membrane” or “equivalent” without naming the manufacturer and model. Two vendors can quote equivalent membranes with 30% different element counts and 50% different service lives, and you cannot compare them.
Should I specify a named membrane or accept equivalents?
Name one manufacturer and model as the basis (e.g. “LG BW400-UD or equivalent”). Accept “or equivalent” only if you also specify the equivalent must be named in the bid with full datasheet. Without that, “equivalent” is a loophole.
What is a reasonable membrane warranty?
3 years pro-rata is standard. 5 years full + pro-rata is premium. Anything less than 1 year is a red flag.
How do I compare bids that quote different scopes?
Decompose each bid into equipment / controls / installation / commissioning and price each line. The lower-cost bid is rarely the lower-total-cost bid once you normalise scope.
How long should the acceptance test be?
7–14 days of continuous operation at design. Anything shorter gives the vendor an out.
Should I require training in the bid?
Yes. Operator training is the difference between a plant that runs at design and one that runs at 60% of design for three years until the membranes are replaced. 2–5 days on-site, included in the bid.
Can the membrane warranty be transferred if I sell the plant?
Usually no, unless explicitly stated. Check the warranty terms before assuming.
Want a procurement spec reviewed before you send it out?
Send us your draft spec and your feed water analysis. We will tell you which lines are weak, what acceptance gates to add, and what to expect on each line in a competitive bid.
Or message an engineer on WhatsApp — we reply within 12 hours (GMT+8 working hours).
About the author: Ella Liu — Industrial Water Treatment Specialist at Rong Water. 10+ years sizing RO, UF, deionised, EDI ultrapure and GMP purified water systems for clients across Southeast Asia, the Middle East, Africa and South America. Connect on LinkedIn or email [email protected].