If the TV is operated by 12 volts and is on the same circuit it could be a low voltage situation.
I would suspect it is electrical noise generated by the motor and a loose connector on a coax is letting the RF (radio frequency) interference do exactly that.
Tighten every connection you can find. If that does not help and you have a switch on a panel you have to activate to turn the antenna amp on watch that light with the water pump running. Try to do this while blocking out any light. Using a cardboard tube from a paper towel roll will do. See if the light dims or flickers. If so, you need to measure the voltage on the back of the panel with the pump running. In this case you will find some additional coax connectors that can be tightened as well. Measuring the voltage on the back of the panel will show if you are getting a low voltage problem that is causing an issue with the tv antenna amp.
This should give you some things to check. Be sure to include any other observations weather you think they are important or not.
H/R Endeavor 2008
Ford F150 toad >Full Timers
Certified Senior Electronic Technician, Telecommunications Engineer, Telecommunications repair Service Center Owner, Original owner HR 2008