Here in Western Oregon, where it rains about 70” to 90“ per year, swimming pools are rare, so rare in fact that we can forget about arriving at a credible contributory value via paired sales, etc. I and several other appraisers I know have for years followed the local assessor’s practice of giving a built-in swimming pool at $5000 contributory value, no matter how large or well built the pool. This is a rule of thumb approach that recognizes the swimming pool as an amenity, but minimizes its contribution given that most swimming pools end up getting filled by buyers who cannot justify the maintenance cost versus the benefits sporadically received.