The peope of Jericho had a problem. The town was in a good location or situation. It seemed like it should be prospering but it was not. You see, there was a problem. The water was bad. The words used to describe it mean bad, evil, malignant, unpleasant, giving pain and barren. That leads some commentators to believe the consumption of this water led to miscarriages and premature births as well as illness and even death.
That would have no doubt caused a lot of people to pack up and leave despite the good "situation" and probably many did but there were some that either couldn't or wouldn't. Perhaps they hoped that things would get better. Perhaps they thought they would be the lucky ones who escaped but still, Jericho remained a town of sorrow, disease and death. Given the present circumstances, it could not prosper. Something had to change.
After Elijah was taken up into Heaven (2 Kings 2:11), Elisha heads for Jericho. While he was there, the people of the city come to Elisha with their problem. He tells them to bring him a new bowl and put salt into it. Elisha then goes to the spring and throws the salt into it and God purified it to this very day.
This may "look" productive but that doesn't mean they are. True and lasting purification comes from God alone.