if zions attackers had red these limits they would've noticed:

"fresh water - official salt concentration limits in drinking water US: 1000 ppm
typical limit agriculture irrigation : 2000 ppm

i assume the "low salt"the shallower zones)of zions well were within those limits or they wouldnt be ''low salt''

there is some salt in the public drinking water in every listed american city as per a site i saw yesterday