61 Pa. Code § 43.3
A water well driller is entitled to an exemption upon his purchase, rental and repair of equipment, materials and supplies used directly in the operation of water well drilling. However, this exemption does not apply to the purchase, repair or service of a vehicle required to be registered under 75 Pa.C.S. §§ 101-9910 (relating to Vehicle Code).
Example 1. Water well driller "W" purchases a back hoe from dealer "X." "W" registers the back hoe with the Bureau of Motor Vehicles. Even though it will be used directly in water well drilling, "W" is required to pay sales tax on the purchase price.
Example 2. Water well driller "W" purchases a drilling rig from dealer "Y." "W" mounts the rig on a chassis, purchased from dealer "Z," which is registered with the Bureau of Motor Vehicles. "W" shall pay sales tax on the purchase price of the chassis, as well as on all repairs and service to the chassis. No tax should be paid on the purchase of, or the repair or service to, the drilling rig.
61 Pa. Code § 43.3