If the cost was less than $2,500 then you can expense it. That includes the cost of the appliance, delivery charges you paid, and any labor cost you paid for professional installation.
One thing to point out here is that if you obtained a new water heater, that does not qualify for the safe harbor de-minimus act, and therefore can't be expensed. So you can't expense a hot water heater. You have to enter it as a rental asset and it gets depreciated over 27.5 years.
WHen expensing this, if you include the sales tax in your cost on the SCH E (and you should) then you can't claim that sales tax anywhere else on your return. Doing so would be double-dipping.