Why don't just dig up the well like the old time??? Simple as that.
There are 90% salt water, it taste like a hell and smell like buffalo's urine. They don't have modern sewer systems, every house dig up the ground to be the toilet. Do you know how many houses are they in each district? More houses is more under ground toilets, more toilets is more under ground water mixed with human stools and urine, that why?
In the old time was small amount people's residents, now the population are blooming and underground toilets are blooming also.