It's under Actor Effects where you need to make the changes, towards the bottom of the list look for the entries WaterHeal1Purified to WaterHeal5Terrible. In each of those entries you can remove the Restore Health effect or simply change the magnitude to 0, although it'd probably be better to remove it. Your character will still probably try to take sip but won't receive any healing, that's hard-coded I believe. This will also remove healing from sinks and....toilets since every non-bottle water source uses the aforementioned entries.
If you have Broken Steel installed then you'll need to make the same changes to DLC03TidalBasinWaterEffect under Actor Effects. With a mod such as this it'd be best if it's one of the last mods loaded as overhauls tend to make changes to the healing effects of water.