I have been doing a bunch of research online into how to build a basement that is below the water table. The common wisdom is to "not waste the money doing that" but as someone who doesn't like to be told no and always likes to fully understand their options, I am curious how I could go about building a basement that is below the water table.
I know it is possible to build a waterproof basement because submarines exist, marinas often build underwater sections of buildings, pools are a thing, etc. The ideal would be to have the primary structure for the basement be poured concrete with no windows or other holes in the walls (plumbing/electricity/air would come in through the ceiling from the higher floors).
For simplicity, lets assume that I don't need sewer out of the basement (perhaps by using an up-flush system to pump sewage/water out). Lets also imagine that the basement is on a flood plain so I can build it while it is dry, but it will be completely submersed in water later in the year.
Finally, again for simplicity lets assume that I am building in a location that has no building codes I need to abide by (so any option is on the table), but I do care about the structure being sound for a long time (e.g., 100 years).
What are the techniques I could use to water PROOF the basement so that it can be fully submerged under water for extended periods of time without leaking?