How does one evaluate the performance of a deep well?

I recently moved onto a property here in Chihuahua, Mexico that has a deep well. The locals say that at about 50 meters one will hit water when drilling, but the supply will be iffy. At 75 meters they say there is a layer of hard rock, but if you get through it they say there is lots of water.

Supposedly the previous owner had a 12" hole bored down to 75 meters. Later he had another driller go inside that casing and go through the rock to 100 meters, putting the pump at 83 meters.

The water comes out of a 1.5 inch line, and a neighbor used it extensively into last summer, sometimes pumping for 24 hours straight. I noticed that the flow diminished considerably, and twice thought that the pump was on and no water was coming out.

Now we have had lots of rain. The water comes out with considerable force and volume. (Where it had taken 2 to 2 1/2hours to fill a large (I guess 300-400 gallon tank) now it fills in in less than an hour.

The water now has obvious turbitity, so I am using a physical and biological filter before we drink it. Before the rains it was clean and clear, even after sitting 24 hours nothing would fall out.

We have a good supply of 220 volt electricity supplied via a properly heavy cable.

How does one evaluate the life expectancy of his pump, and the supply of water in the well? Where is a good place to send water for testing for suitability as drinking water?

I am no geologist, but the land, dirt, mountains and plants is very similar to what one would find around Pecos. I believe that northern Chihuahua to the east of the "Rockies" is part of the same geological formation and area as is West Texas.

Any thoughts?

Walt Barbier