Non potable water

You might want to contact your ayuntamiento. Firstly to find out IF you can fill (due shortage of water), and if you can fill, they have information of whom to contact.

You can fill your pool from a tanker as long as the water is from natural sources.

Sergio Inox has springs on his land and will supply, he has a Facebook presence 

"Supply of drinking water transport ferre 722289639 water supply for swimming pools, home delivery on route, cans, works and services quality and good taste mineral water directly from the mountains"

HTH

John