Simon Sakhel waste water cost evaluation tools are available online and one can easily understand this based on the rough estimates as I personally took help twice and found it to be quite reliable but depends on + - 15% variations which you have to consider on the plus side and make your assumptions.

I don't think the cost of water treatment equipment is related to the quality of the wastewater.

As a general rule, the total annual cost is a function of the construction cost of sewage treatment plants, the operating cost for the aqueduct, the operating cost for sanitation, the product of the length of the sewer pipes to be replaced by the cost of replacing the sewer pipes, the cost of repairing the water supply pipes, the interest rate, the lifespan of the treatment plants, the construction cost of the water treatment plants drinking water, service life of drinking water treatment plants, cost of construction of pipes, the service life of pipes.

The calculated annual cost is then divided by the annual production of drinking water on the territory of the city considered in order to estimate the volumetric cost associated with drinking water.

Regards

I think it depends on the situation. The standard situation has been well described by Bachir I think.

However, if You are in a water scarcity situation You can start calculating the value (and the acceptable costs) considering a reuse situation. e.g. against seawater desalination, long pipelines to the next water regions with abundance of water.

E.g. Copenhagen is overusing natural water resources. There are three alternatives: Desalination of Seawater, building a pipeline to Sweden (Gotenborg area) or indirect reuse.

Desalination will get expensive, serving the capital of one country with another countries groundwater resource might be politically fragile so if enhanced wastewater treatment and indirect reuse can beat the price for desalination there is a deal.

Simon Sakhel

I agree with Bachir that the cost of wastewater equipment does not directly relate to the wastewater quality but mainly to the kind of wastewater (municipal sewage, various kinds of agricultural and industrial wastewaters) and the required quality of the treated water which determine the wastewater treatment sequence and process steps and its daily loads (hydraulic, organic, nutrients, ...) which determine the sizing of the process steps with their equipment including the levels and extent of the process monitoring and controls.

After this assessment and preliminary process design work has been done, then the CAPEX and OPEX can be calculated according to the local conditions.

I agree the colleagues saying it is not easy to define treatment cost. Usual index would be $/m3 but it really depends what are we calculating into the price (collection? treatment? polishing? rainwater?), to what extent are we treating to (country/local effluent limits, reuse as irrigation, reuse as grey water, reuse as drinking water), what exactly are we starting from (storm water, municipal, light or heavy industrial water), what technology are we using (a constructed wetland with one half alcoholic operator or reverse osmosis with a smaller nuclear power plant next to it to feed it with electricity), or, maybe, how much we care about the regulations (Oslo city center vs East-Siberia gas rig on the taiga).

Every site requires their identical calculations, and those can be compared. Or, at least, similar situations should be compared.

I don't envy marketing guys/gels here as they have to say something to sell a project, and later on they have to force their employing company to keep the word they given to the client...