The drinking water distribution network total length is about 2,295 km (1,426 mi, or the distance from Milan to Cairo), reaching more than 50,000 end users and with a total demand coverage. The web-like network follows the City’s street layout and consists of pipes with diameters ranging from 80 to 1200 mm (3.15 to 47.2 in).
The network is made solely of metals such as steel (15 percent), used mainly for large pipes which, since the 80s, has partly replaced grey iron (65 percent) and ductile iron (20 percent), two materials with good corrosion resistance and a wide range of special pieces readily available on the market.
The pipes carry the waterworks water to the connection point of each building with a cut-off valve and a water flow rate metre recording consumption. The internal condominium network in buildings distributes water to apartments.
The drinking water pipes are laid on average about 1.5 m (5 ft) below ground, to protect the water from changes in temperature; this means the water temperature remains constant at 14°C to 15°C (57 degF to 59 degF), to the point where it is delivered to the internal condominium systems.
MM maintains the network regularly to minimise leaks which in Milan amount to 14 percent against the Italian average of 30 percent.
Maintenance of the water supply network consists of a number of activities:
- scheduled maintenance carried out on the entire network every year, to identify problems in the network, prevent break-downs and leakage. From 2004 to 2008, Metropolitana Milanese replaced and expanded a total of about 40 km (25 mi) of the waterworks network;
- carrying out new connections and replacing corroded ones;
- emergency operations in response to user calls through the Emergency Service are carried out entirely by the in-house staff, available 24/7.
In the selection of maintenance methods to be used, Metropolitana Milanese follows closely new developments and technologies and seeks alternative solutions to traditional excavation which has both a high environmental impact and high costs.
Metropolitana Milanese has started repair operations on existing networks using non-invasive technologies (e.g. no-dig operations using the "cement mortar line" technique) allowing pipe repair instead of renewal. Since 2010 the relining of existing steel pipes with the high-density polyethylene (HDPE) has started, without digging them out.