Artesian water is water that naturally comes up out of the ground. This is because it is stored in an underground aquifer which is under pressure. The pressure is created by water entering the aquifer from a higher level e.g. surrounding hills and being restrained there by a layer of impervious clay or rock. Should the impervious layer be punctured by drilling through it, the water will be forced up the borehole to emerge above ground, sometimes with enough pressure to form a fountain. see below
Artesian water may be a resource, if the water quality is good and there is a need for it, for example, for irrigation. Sometimes however, it can be a nuisance, e.g. if the unwitting driller of a geothermal borehole unexpectedly hits a strong artesian source whilst drilling in a town suburb. (No, it hasn't happened to us, but it has happened)
Unwelcome surprises can be avoided by getting a geological report before the borehole is drilled. Synergy also has experience of the areas where artesian conditions may be expected. We know how to deal with these situations without making the client "famous".