Hi Barry
I live in Villamartin whiich is near La Zenia
The pipe which goes into the water meter, (found in the community water cupboards) has the size embossed on it.
With ours, the 20mm ones are green while the 13mm ones are smaller.and, I think, silver in colour.
If you look at the bottom line on your Aquagest factura the first figure on the left denotes the size of the supply. you are paying for.
There does not appear to be any reason why some have one type and some the other. Some 1st floor apartments have
20mm whilst others have 13mm . Each type of house, big or small have both types.
I have been trying to get mine changed for nearly two years, and had worked out that I would save around 200 Euros per year.
Regards
June