It's municipal town water ,
I bought it from my LFS .
Actually a very reliable friend that sells corals , fish and some supplies from his house .
I think it was used but he did check it ,
It ran good for him .
0 TDS out
According to the manual "pressure below 40 psi, or a pressure drop of 15-20% of normal water pressure indicates the prefilters are in need of replacement ". Of course this all depends on the pressure of your city water. If you remove the two pre filters then the Guatemala will read your water pressure.