Determining the discharged volume

To calculate the fee for sewer and treatment services, the discharged volume must be calculated. The discharged volume is considered to be equal to the volume of water withdrawn from the aqueduct, by taking measurements at the discharge point with meter installation, in the presence of private drawing points or production processes that decrease or increase the amounts of water discharged compared to the water withdrawn.

Any discharge without a gauge will be progressively equipped with a discharge meter; in the meantime, we will calculate the discharged volumes using an estimate, calculated on the basis of the technical report sent by the discharge owner to and accompanied by the following documentation:

MUD (Environmental Declaration Form) and/or copies of liquid waste disposal forms;

Water balance with readings of the aqueduct and well meters (consumption and photos of the meters), readings of internal gauges if installed (consumption and photos of the meters), calculation of the amounts dispersed in the product based on the "recipes” and production in the reference period, the technical specifications of the machines and equipment that generate a water dispersion (reports and specifications provided by the manufacturer).

No flat-rate, estimated and percentage deductions shall be taken into account, nor others not accompanied by the documentation requested in the previous points. The technical report must be sent at least once a year by 31/01 of the subsequent year.

Autonomous supply sources

If you source all or part of your water from sources other than the public aqueduct network, you will need to install the instruments to measure the amount of water withdrawn and care for them at your own expense. The measurement instruments must be compliant, arranged for remote reading and placed immediately downstream of the withdrawal point, before any possible branches.

In addition, if your supply comes entirely or partly from autonomous sources other than the public aqueduct network and if you even partially discharge the withdrawn water into the public sewers (also in the case of only domestic discharges), at least once a year you must send a declaration of the volumes withdrawn with the following information: SIF identification code or other identification code of the withdrawal point, type of meter installed, make and serial number of the meter, reading detected on 31/12 of each year, cubic metres measured on 31/12 of each year, photograph of the reading on 31/12 of each year.

Discharge gauge installation


Discharges with a minimum daily volume greater than 15 m3/day or annual volume greater than 3,000 m3/year, and when deemed appropriate, must have a discharge gauge.

You can request its installation by sending an email to

We reserve the right to evaluate the technical feasibility of the installation, accept the request and identify the type of gauge to be installed. The costs for the installation of the measurement instruments are borne by the discharge owner, as indicated by the price list approved by the Division Office of the Metropolitan City of Milan.

Gauge malfunction

If you notice irregularities in the gauge's operation, notify us by sending an email to or by calling our toll-free number 800.428.428: we will proceed with the verification of the gauge.

If the gauge is faulty or malfunctioning, we will activate the procedures for the correction of any incorrectly measured discharged volumes and for its replacement, free of charge, except in cases where the malfunction or breakage of the gauge is the responsibility of the customer.

For more information

We are as transparent as our water: that's why we are always available for any need.



Analytical calculations

We carry out a number of analytical calculations, identified on the basis of the maximum daily or annual volumes discharged, in order to verify compliance with the acceptable limits of discharged water and to identify the concentrations of pollutants for the purpose of calculating the fee for sewage and treatment services.

The number of analytical calculations carried out is calculated according to the following table:

Discharged volume Annual analytical calculations WITHOUT hazardous substances Annual analytical calculations WITH hazardous substances
< = 15 m3/day and <=3,000 m3/year 0 1
16-100 m3/day or 3001 -25,000 m3/year 1 2
101-400 m3/day or 25001 -100,000 m3/year 2 3
> 400 m3/day or > 100,000 m3/year 3 4

Sampling analysis and validation

The analytical calculations are carried out in accordance with APAT/IRSA procedures and the relevant regulations in force.

You can participate in all the phases of the control, including sampling, sample opening and performing the analyses. In addition, the owner of the discharge may submit his/her observations on the representativeness of the sample for tariff purposes. We may evaluate the appropriateness of not using the results in the tariff calculation and carry out control samples at a later time, if deemed consistent with the process or motivated by resolved malfunctions, of which the owner is required to transmit the relative documentation.

The request must be submitted in writing within 15 working days from the communication of the analysis results, by sending an email to Once the terms have expired, the analysis is considered approved by the customer and valid for the tariff calculation. If a written request is received, we undertake to provide a reasoned response within 20 working days.

If an analytical calculation shows a concentration of pollutants exceeding the acceptable limits, we will perform a second analytical calculation within 60 days. We can also carry out more frequent controls for environmental purposes and to protect our treatment processes. In the context of these controls, compliance with the quality limits allowed for discharge will result in the suspension of the application of the penalty.

Pollutant concentration

The concentrations of the main and specific pollutants used in the tariff formula are calculated as the arithmetic mean of the values obtained:

from the 3
most recent samplings

with a maximum of 3 analytical calculations per year.

from all
the samplings of the year

with more than 3 analytical calculations per year.

Unsupervised analysis

You can send us the qualitative analyses on the unsupervised sewage discharged (carried out according to APAT IRSA-CNR 29/2003 as amended or the regulations in force) only if the analyses relate to authorised discharges deriving from heat exchange operations, indirect cooling, MISE and MISO or are related to discharges for which no excess of the discharge limits has been found in the last 24 months.

We reserve the right to accept unsupervised quality analyses to the maximum extent of:

  • 1 analysis every 12 months where a minimum of more than 2 calculations per year is foreseen; 
  • 1 analysis every 18 months, where a minimum of 2 calculations per year is foreseen;
  • 1 analysis every 36 months, where a minimum of up to 1 calculation per year is foreseen.

The unsupervised qualitative analyses must be sent to and can be validated by us and used for tariff purposes only if carried out according to the APAT/IRSA timelines and standards or the regulations in force, and if the results of the analyses do not show deviations greater than 30% for each pollutant analysed, compared to the arithmetic mean of the 3 most recent samplings, or where not available, 3 analyses of the mean of analyses available.

For clarification

We are as transparent as our water: that's why we are always available for any need.

phone number


Discharge fees

The fees for the collection and treatment service for industrial users are divided according to a formula that includes the sum of a fixed component (QF), a capacity component (QC) and a variable component (QV).


Fixed component (QF)

This is calculated on the basis of the minimum number of annual analytical calculations for the discharge point provided for by the ARERA resolution, according to the amounts discharged and the presence or absence of hazardous substances in the discharged volume.

How the discharged volume is calculated

Discharged volume Annual analytical calculations WITHOUT hazardous substances Annual analytical calculations WITH hazardous substances
< = 15 m3/day and <=3,000 m3/year 0 1
16-100 m3/day or 3001 -25,000 m3/year 1 2
101-400 m3/day or 25001 -100,000 m3/year 2 3
> 400 m3/day or > 100,000 m3/year 3 4

Capacity component (QC) and variable component (QV)Pollutants

The capacity component is quantified on the basis of the maximum envisaged concentrations of COD and suspended solids and the maximum volume authorised for discharge, while the variable component is calculated on the basis of the quality of the sewage and is proportional to the discharged volumes.


The concentrations of pollutants are calculated with an arithmetic mean taken from the values obtained from the 3 most recent samplings (where up to 3 analytical calculations are carried out per year) or from all the year's samplings (in the case of more than 3 calculations per year).

The rates, coefficients and reference parameters approved by the Metropolitan City of Milan Authority for the calculation of the fee are published annually on BURL and can be requested by writing to


The table lists the values ​of the surface water discharge limit and the cost percentages

Parameters Value (mg/l) % of cost
COD 160 52%
SST 80 28%
Total Nitrogen (N) 10 15%
Total Phosphorus (P) 1 5%
Chromium (Cr) 2 16,50%
Chlorides (Cl-) 1200 2,50%
Sulphates (SO4-2) 1000 10%
Sulphites (SO3-2) 1 10%
Total Surfactants 2 1,50%
Aluminium (AI) 1 1,50%
Iron (Fe) 2 1,50%
Manganese (Mn) 2 1,50%
Animal and vegetable fats and oils 20 5%

Cost constraint for each customer

Pursuant to the provisions of resolution ARERA 655/2017/R/idr, the annual expenditure of each industrial customer, with the same amount of sewage discharged (volume and quality characteristics), cannot be increased by a value greater than 10% per year compared to the expenditure incurred with the method previously in force.

For clarification

We are available for any need, contact us for further details and clarifications.

phone number

02 89520267