many thanks for quick answer and wide explanation.
I don't expect that are many electronics who can survive direct strike of lightning :-( We had in our marina yacht who was hit directly into mast on the bay and EVERY electrical ans electronic devices on board was totally burn out including cables, batteries, engine alternator.....
So I'm fighting only against inductive currents.
Very interesting observation according to moving magnet. Hope that will be not a problem in my case. The sensor is installed under pier between stilts where water is relatively calm.
Here are in Poland on Baltic we have no tides at all, but when there is strong wind coming from the sea we have backflow of water and the level is increasing some times very high. So the my sensor is to alarm the marina stuff and yacht owners on that situation.
Also in my design I have no loops inside the pipe - I designed a kind of modular PCB for having reed switches distributed evenly. There are only switches without coil of course. One module is 250mm long with 5 switches and I have 6 modules 1,5m long sensor. At the end of module there is small snapp-off PCB with the DS2438 and surrounding components.
I will install the sensor next week and we will see.
Here you have some pictures to show schematic and my idea of design.