Many digital tuners especially early units were more prone to interference than new ones. I'm certain most experienced interference from dryers, lights, blenders lightning with early TV's or digital set top boxes in their houses a lot in the early days of Digital TV. Mine used to crack loudly and loose signal. New tv's seem to have fixed this.
However any device with a inductive load(ie flourescents/electric motors etc)has the potential to create a substantial spike upon breaking the contact
Every time the contacts make or break there is a small arc.It is this arc that radiates the interference that causes the problems. (Hence that spike when the tap is turned and the pump activates.)
You can try to eliminate the problem with sheilded cables, better reception (bit hard that one but a good candidate) seperate power supply from thE battery/setec. Move thE TV away from the water pump, which in mine is 400mm away from the winegard.
Saying all that I would try first plugging your TV power supply in to a seperate power supply for testing. Such as a spare battery, or a 240v supply from the house direct. If you still get interfernece it is signal related and not power supply related.
You can then rest assured that power supply cabling /plug/ joiners, terminals are not the culprit.
If you know someone borrow their 12v TV and try it in the same spot.
Here's an interesting find on google:
The introduction to Digital signal may mean many caravans will have wiring of TV cable installed that is not satisfactory for digital. The Australian standard for digital & satellite is AS1367:2000. This is not an enforceable standard, but anyone connecting TV installation domestically knows that use of screw "F" connectors & use of RG6 or RG59 coaxial cable is the required standard and is critical. (FOX TEL only use this "F"system)
Most caravan manufacturers are still installing the "PUSH IN" fittings & this more than certainly will have the potential to cause problems when tuning to digital signal through set top boxes. Discuss this when ordering a new van. Certainly, flat ribbon cable should not be used & should be replaced. A report on this subject is available, obtained independently from GME Kingray.