Answer:
It happens because the consuming is higher than the water drop rate, or even because there are too many people in a zone where there is not enough fresh water.
Oil still plays an important role in the global economy despite the continued efforts to reduce its use and to find alternative green energy sources. In the early days, finding oil during a drill was considered somewhat of a nuisance as the intended treasures were normally water or salt. It wasn't until 1847 that the first commercial oil well was drilled in the Absheron Peninsula, Azerbaijan.1 The U.S. petroleum industry was born 12 years later, in 1859, with intentional drilling near Titusville, Pennsylvania. (Drilling in the United States began in the early 1800s, but they were drilling for brine so any oil discovery was accidental.)2
