When it goes down it will drop at a value equal to 1-([[Faith]]/200). Thus, at 0 faith one would lose 1.0 alignment and at 100 faith one would lose 0.5 alignment.
This loss is halved in local range to the White light for white lighters.
If your alignment drops below 1 as a whitelighter, you will lose your faith.
Gaining alignment points (either positive or negative) has a cool down timer. Once you have gained alignment you have to wait 30 minutes before you can gain again. Note that alignment automatically drifting towards zero does not affect this timer.