That is a great question...curious - are you asking from a buyer's perspective or seller's perspective?
On paper for appraisal purposes, a pool is worth pennies on the dollar in terms of the cost to install a pool. So if a pool cost $50k to install, one can not assume that it adds $50k to the value of the house. Perhaps it adds $10k?...or just sways a buyer to choose the house with the pool vs. an identical home sans pool. Much depends on the rest of the house - size of the home, size of the remaining yard, what is typical for the neighborhood, etc.
Many buyers are adamantly opposed to purchasing homes with pools (have kids they do not want near a pool, cost and trouble to maintain are too much, etc.), while others are delighted to find a home with a pool.
Good luck to you.