Reserves and Taxes, how does it work?

[Royston McKaig]

What's up everyone. I have been lurking around for while and I have a question I can't find the answer to.

Lets say I am renting out a home for $1,000 a month and I am setting aside 25% (lumped CapEx, Maintenance, Vacancy).

At the end of the year, I have a reserve of $3,000 designated for a certain purpose. Now let's assume I didn't have to spend a dime of this money. If this money is taxed, my reserve has been slightly diminished by the amount of tax paid.  Is it possible to avoid this? Can I itemize/label/categorize this money so the IRS knows this is for a rainy day?  

Thanks everyone, these forums have already provided a wealth of information!