Denryan,
Do you know for certain if the water is of POTABLE quality ?
As I have been sold Agriculture quality water before,when I had required Potable quality,by a local Spanish man.
This appears to be quite a lucrative trick,as the price difference between the two types of water is quite large.
It has certainly happened to most people living in the Campo and not on mains supply,as you probably would not be able to physically detect any difference.