The Pool of Reflection is a new feature to be introduced in Diablo III: Reaper of Souls. It has the same graphics as a Health Fountain, except it is gold-colored. The buff provided by this Pool of Reflection increases XP (experience) by 10% of your XP, stacks up to 10 times and persists through logouts. However, the character loses the buff in death.
[bluepost]Grimiku: The length of the Pools of Reflection buff should be about 10% of your total xp to your next level, and that can stack up to 10 times. I'll quote a post made by Nevalistis since she did a good job of explaining the buff.
Nevalistis: Also, while the basic percent bonus doesn't increase with additional Pool of Reflection buffs, the length of the buff does effectively stack each time you claim an additional Pool. The amount of bonus experience you can benefit from should show up when you hover over your experience bar, and this value will increase by about 10% of the current experience required for your next level/Paragon level for each Pool claimed. This bonus persists on logout, but is lost upon death.