If you rent part of your primary residence, you can expense a portion of your repair expenses as long as they pertain to the entire property.
But it will also be important to determine if this is a repair or an improvement. A repair restores property to as-is or as-was condition, and repairs can be expensed. An improvement is a betterment -- it makes the property more valuable, or extends the useful life of the property or one of its subsystems.
For example, fixing a hole in the roof caused by a tree branch blown down by a storm is a repair. Replacing the entire roof with new 30-year shingles is an improvement.
The part of the improvement that can be allocated to the rental is depreciated over 27.5 years, the part of the improvement allocated to your personal residence is not deductible, but it increases the cost basis of the home and may reduce your capital gains when you sell.
You can only expense a portion of repairs if you actually rent out the room at market rates. And the depreciation has to be repaid (recaptured) so the advantage of depreciating an improvement is fairly small in the short run. (Note, however, that when selling, you have to repay depreciation you took or could have taken, even if you didn't take it.)
And I believe some of the rules are different when renting a part of your residence, as opposed to renting a separate property.
Most important I would think, is whether fixing the pool will be personally enjoyable, or will help you sell the property if you really plan on selling in a couple of years. The tax consequences are likely to be only very modestly in your favor if at all.
@Carl ?
