Installing a swimming pool for medical reasons sounds unusual, but the IRS does sometimes allow a deduction when the circumstances are right. If a doctor prescribes hydrotherapy or aquatic exercise as a treatment for a specific medical condition, part of the cost of installing a pool may qualify as a medical expense. You can generally deduct the cost that exceeds the amount by which the pool increases the value of your home. For example, if the pool costs $30,000 to install but adds $20,000 to your home's value, the deductible amount is $10,000. You would still need to itemize and exceed the 7.5 percent of adjusted gross income threshold, but this is one of the more interesting medical deductions that courts have upheld.