How can we get maximum life of a water well?
Since you are asking about a very old well in your comment , how long can a well last? There are water wells still in use today from biblical times.
If they are deep enough and have not been contaminated by surface water or things being dumped in them the well will last as long as there is water. 
You would want to have a sample tested to make sure the water is safe to drink but if the water is good I would use it without question.