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Combined RO and DI
RO-DI Water Systems for Laboratories
RO-DI water systems combine reverse osmosis with deionisation in one unit. The RO stage removes 96 to 99 percent of dissolved salts, and the DI stage polishes the remainder to final quality. Putting RO first is what makes the DI resin last, since cartridge life is consumed by ionic load.
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Answer first
What RO-DI Water Systems Are, and How They Are Specified
RO-DI water systems combine reverse osmosis with deionisation in one unit. The RO stage removes 96 to 99 percent of dissolved salts, and the DI stage polishes the remainder to final quality. Putting RO first is what makes the DI resin last, since cartridge life is consumed by ionic load.
The two stages do different jobs and the order matters. RO is bulk removal and its consumable is a module lasting years; DI is polishing and its consumable is resin consumed in proportion to the ions arriving. Running DI on raw water exhausts cartridges in weeks.
That is the whole economic case for the combination. Cutting the ionic load by one to two orders of magnitude before the resin sees it extends cartridge life proportionally, which is usually the difference between an affordable running cost and an unpleasant one.
Specification
RO-DI system configuration
| Stage | Function | Consumable and basis |
|---|---|---|
| Pre-filter | Particulate removal | Cartridge, 4–12 weeks by differential pressure |
| Carbon | Chlorine removal before the RO membrane | Cartridge, 3–6 months by downstream chlorine test |
| RO module | Bulk salt removal at 96–99 % | Module, 2–3 years typical in laboratory duty |
| DI cartridge or pack | Polishing to final quality | Resin, consumed by ionic load not by time |
| UV where fitted | Microbial and TOC control | Lamp, around 9,000 h |
| Final filter | Particulate and microbial barrier at dispense | 0.22 µm, 6–12 months |
Pre-filter
- Function
- Particulate removal
- Consumable and basis
- Cartridge, 4–12 weeks by differential pressure
Carbon
- Function
- Chlorine removal before the RO membrane
- Consumable and basis
- Cartridge, 3–6 months by downstream chlorine test
RO module
- Function
- Bulk salt removal at 96–99 %
- Consumable and basis
- Module, 2–3 years typical in laboratory duty
DI cartridge or pack
- Function
- Polishing to final quality
- Consumable and basis
- Resin, consumed by ionic load not by time
UV where fitted
- Function
- Microbial and TOC control
- Consumable and basis
- Lamp, around 9,000 h
Final filter
- Function
- Particulate and microbial barrier at dispense
- Consumable and basis
- 0.22 µm, 6–12 months
Indicative configuration. Stage arrangement and consumable life follow the datasheet of the system quoted.
Selection guidance
If DI cartridges are costing too much, look at the RO stage first
A rising DI cartridge bill is almost always a symptom rather than a cause. Cartridge capacity is consumed by ions, so if consumption has increased it usually means more ions are getting past the RO stage than used to.
Check RO permeate conductivity against its commissioning figure before ordering more cartridges. A degraded RO module, chlorine damage from an exhausted carbon stage, or simply a change in the incoming mains water will all show up here — and replacing the RO module is frequently cheaper than absorbing the cartridge consumption it is causing.
Application mapping
Where RO-DI Water Systems Are Used
General laboratory supply
- Typical requirement
- Type II or III at moderate volume
- Indicated configuration
- RO-DI unit with storage sized on peak draw
Feed to Type I polishing
- Typical requirement
- Consistent low-conductivity store
- Indicated configuration
- RO-DI base with point-of-use Type I polishers
Teaching laboratories
- Typical requirement
- Dependable output at controlled running cost
- Indicated configuration
- Compact RO-DI sized for peak class use, consumables planned annually
Replacement and consumables
Replacement Intervals and the Signs It Is Due
Intervals are indicative planning figures. The signal in the last column is what should actually trigger the change.
| Item | Typical basis | Signs it is due |
|---|---|---|
| DI cartridge | By ionic load — feed conductivity × volume | Outlet conductivity or resistivity breaking through |
| RO module | 2–3 years typical | Permeate conductivity rising against commissioning figure |
| Carbon cartridge | 3–6 months | Free chlorine detected downstream |
| Pre-filter | 4–12 weeks | Differential pressure rise or flow decay |
| Final filter | 6–12 months | Flow decay at the dispense point |
DI cartridge
- Typical basis
- By ionic load — feed conductivity × volume
- Signs it is due
- Outlet conductivity or resistivity breaking through
RO module
- Typical basis
- 2–3 years typical
- Signs it is due
- Permeate conductivity rising against commissioning figure
Carbon cartridge
- Typical basis
- 3–6 months
- Signs it is due
- Free chlorine detected downstream
Pre-filter
- Typical basis
- 4–12 weeks
- Signs it is due
- Differential pressure rise or flow decay
Final filter
- Typical basis
- 6–12 months
- Signs it is due
- Flow decay at the dispense point
DI cartridge life varies directly with the ionic load reaching it, so a change in RO performance changes the cartridge bill immediately.
Put this on a standing order
Once a plant has a year of running behind it, consumption for this item is predictable. Sending the plant list and last year's usage gets it scheduled against your maintenance calendar instead of ordered in an emergency at the point the plant is already out of specification.
Commercial terms
How This Category Is Quoted
Water treatment does not have a list price, and any supplier quoting one before seeing a feed analysis is quoting a different plant from the one you need.
Pricing basis
On request, and capacity-dependent. Plant pricing moves with capacity, feed water analysis and the recovery target; membranes, cartridges and resins are quoted per element, per lot or per litre of media.
Order quantity
From a single replacement element or a case of cartridges through to full plant scope. Consumable lines are quoted per box or per lot, and the lot size is stated on the quotation.
Lead time
Confirmed per line item at quotation stage. Stocked consumable lines and made-to-order plant differ substantially, so a single blanket lead time for the category would be misleading — the quotation carries the figure for each line.
Invoicing
GST invoice against company or institutional purchase order. Proforma issued where advance payment or internal approval requires it.
Delivery coverage
Despatch from Delhi NCR across India, including plant, project and institutional sites. Delivery city and site access are asked for at enquiry because both affect despatch mode.
Documentation
Technical datasheet for the item quoted, and a test certificate where the principal supplies one with that product. Tender and institutional documentation formats are prepared on request — send the format with the enquiry so the quotation is issued in a form you can submit without rework.
Request for quotation
Request a Quote — RO-DI Water Systems
Fields marked with an asterisk are required. The technical fields are what usually decide whether you get a quotation on the first pass or three emails of clarification.
Frequently asked
RO-DI Water Systems — Common Questions
Why combine RO and DI rather than using one of them?
Because they are complementary. RO removes 96 to 99 percent of dissolved salts economically but does not reach final laboratory quality; DI reaches it but is consumed in proportion to the ions arriving.
RO first cuts the ionic load by one to two orders of magnitude, which extends DI cartridge life proportionally and makes the running cost acceptable.
How long does a DI cartridge last on an RO-DI system?
It depends on ionic load — RO permeate conductivity multiplied by the volume dispensed — rather than on elapsed time.
If cartridge life has shortened, check RO permeate conductivity against its commissioning figure before assuming the cartridge is at fault.
What quality does an RO-DI system produce?
Typically Type II or Type III depending on the configuration and the feed. Reaching Type I at 18.2 megohm-centimetre needs a dedicated polishing stage at the point of use.
State the grade and the parameters your methods depend on at enquiry rather than the grade alone.
Related Products and Categories
Specified alongside ro-di water systems, and the category this page sits in.
Type I ultrapure water systemsType III RO water systemsDI water systems at plant scaleBack to Laboratory Water Systems
- Delhi NCR base with pan-India supply, including plant and project sites.