He wiped down the back wall where the mold had sunk in (to what extent I'll never know) with chlorine bleach and called it a day. 

Unless you are looking to build something extravagant and large with a unique design.Also, there is a LOT to consider regarding sand filter or regular filter, backwash line ran, pool pump (variable speed or single), pool heater (Gas vs electric and the kWH of the heating elements), whether doing a salt water system, something like a drinkable pool water system, or typical chlorine pool (which will often need a chemical feeder).Also dehumidification is important.

That can be as cheap as a simple filter or chlorination system or as expensive as relocating and drilling a new well.

Over time, the finish broke downThat is a normal wear pattern of filth tracked into the room and ground into the oak over time, and it was repeatedly washed with chlorine bleach, which further dissolved the wax paste helped along by sunlight, as David pointed out. 

Deterioration linked to chlorine water additives has been linked to the failures, however customers on private water supplies have reported many problems.

It's about ~300 per year for maintenance contracts and an extra ~70 per quarter for chlorine tablets (sprinkler only, usually).  

It's made of polybutylene and chlorine destroys it.  

Wear a respirator and something to protect your eyes from the chlorine vapors.David J Dachtera"Success is not a destination.

The H2O Solutions people got us set in a day by changing from chlorine to peroxide.

I had a liquid chlorine feeder that would take 4 gallons of liquid chlorine and inject it when chlorine was low.