Water balance by country · Updated 2026-09-30
Perdite idriche in Italy: ARERA's M1 macro-indicator, ISTAT losses and the IWA water balance
How Italian water operators calculate the IWA water balance for ARERA's technical quality regulation (RQTI) — the M1a linear and M1b percentage loss indicators — and how ILI and litres per connection compare.
Calculator settings for Italy
- Units
- Metric — ARERA reports m³/km/day (M1a) and % (M1b)
- Benchmark category
- Standard
- Meter location
- At the building; 2–8 m service pipe; condominium bulk meters common
- Supply
- Continuous in the north; intermittent (turnazione) in parts of the south and islands
- Reporting
- ARERA RQTI macro-indicator M1 (M1a linear losses, M1b percentage losses); ISTAT census of water services
Italy loses over 40% of the water put into its distribution networks according to ISTAT — among the highest in Western Europe — and the national regulator ARERA has made loss reduction the first of its technical-quality macro-indicators. Every operator is classified on M1, which combines linear losses in cubic metres per kilometre of network per day (M1a) with percentage losses (M1b), and must improve by a set percentage each year or face penalties.
Mapping ARERA's indicators
| ARERA / ISTAT measure | In this calculator |
|---|---|
| M1a — perdite idriche lineari (m³/km/giorno) | Water losses per day ÷ km of mains (the calculator reports real losses per km per hour — multiply by 24) |
| M1b — perdite idriche percentuali (%) | Water losses ÷ system input volume |
| Volume immesso in rete | System input volume |
| Volume erogato / fatturato | Authorised / billed authorised consumption |
| Perdite reali / apparenti | Real / apparent losses |
ARERA's linear indicator is closer to the IWA's litres-per-km measure than to the ILI. Both are reported here, and the ILI adds the pressure and connection-density normalisation that a per-km figure lacks — useful when comparing dense northern networks with sprawling southern ones.
Italian specifics
- Condominium metering: many apartment buildings have one bulk meter and unmetered internal distribution. Count the building as one connection and its bulk meter as the customer meter.
- Service pipes run from the street main to the building; 2–8 m is typical.
- Turnazione (rotating supply) in Sicily, Calabria and parts of Puglia requires the supply-hours correction.
- Many networks are gravity-fed from mountain springs with minimal treatment — 'basic' for carbon; pumped groundwater and river abstraction are 'traditional'.
- High-pressure networks in hilly cities (Genoa, Naples, Palermo) make pressure management the first lever; enter pressure by district.
Typical results
Northern operators (Milan's MM, Turin's SMAT, Hera, Iren) report losses of 15–30% and ILIs around 2–4. Southern and island systems often exceed 50% losses with ILIs above 8. ARERA's classes A to E on M1 correspond roughly to the World Bank bands the calculator uses, so the results page gives a useful preview of where an operator will land.