Industrial reverse osmosis cost per usable m³

Define the boundary before comparing unit costs

A quoted figure becomes useful when its boundary is clear. Does it start at mains water, a well or an upstream treatment outlet? Does it end in the permeate tank or at the point of use? State delivery pressure, water quality and availability. Plants with identical nominal flow can supply different quantities of usable water.

Separate treatment operating cost, purchased-water cost and total cost including capital. The EPA RO/NF cost model provides a way to organise cost items. Its US drinking-water cost assumptions are not prices for an industrial installation in Spain.

Recovery determines purchased-water demand

At recovery Y, feed flow Qf = Qp / Y and concentrate flow Qc = Qf − Qp. Delivering 10 m³/h of permeate at 75 % recovery requires 13.33 m³/h of feed and produces 3.33 m³/h of concentrate. Each cubic metre of permeate therefore needs approximately 1.333 m³ of feed and generates 0.333 m³ of concentrate.

This simplified balance excludes flushing and off-specification water. Add those uses and deduct rejected product in the actual budget. A higher recovery is useful only if concentrate chemistry and membrane operating limits allow the plant to sustain it.

An OPEX example with explicit assumptions

This original calculation describes a hypothetical brackish-water RO plant without additional washwater or distribution losses. Every price and consumption figure below is a teaching assumption, not a current tariff, a Neptuno quotation or an equipment performance claim. Recovery is 75 %, and the denominator is useful permeate.

Explain whether purchased water is included

In the example, operating cost excluding purchased water is €0.60/m³; including feedwater it becomes €2.20/m³. Both figures are valid within their stated boundary. Using only the first as the cost of produced water would hide a decisive expense. At 40,000 m³ of useful annual output, the operating total would be €88,000 before capital, financing and taxes.

If concentrate can serve another process, credit only the savings actually achieved and subtract adaptation and control costs. Avoid simultaneously claiming disposal and water-purchase savings that depend on incompatible uses of the same stream.

Add capital and check useful operating hours

Levelised total cost adds annualised capital to annual operating expenditure and divides by useful annual output. An initial simple view may show investment divided by expected life; a purchasing decision should account for discounting, replacements and residual value consistently across offers.

Rated capacity is different from annual demand. Shutdowns, seasonal use, cleaning and insufficient storage reduce the volume available to absorb fixed costs. Request production at the project feed quality and temperature, including the most demanding design condition. Specify whether energy figures include pretreatment, feed pumping and delivery pumping; otherwise those duties can disappear between supplier boundaries.

Request the information needed to compare offers

Ask for a flow balance, estimated power and energy with their boundary, chemical consumption, expected cleaning intervals, replacement allowances and included services. Mark each number as measured, calculated or assumed. Obtain local disposal costs before treating concentrate management as a minor allowance.

A useful sensitivity analysis changes water price, recovery, energy, concentrate cost and annual utilisation. This shows which uncertainty deserves better sampling or a trial before equipment investment is fixed. Update the model when pilot information or site quotations replace the initial assumptions.