"Irish Water" coming from N.I.It says that it is Irish water.
but the clue would be in the area the spring is located.
I think you may be a little optimistic thinking this is spring water. It's more likely to be processed tap water.
They take water straight out of the mains supply, purify it and then re-mineralise it to give it taste etc.
I'd be surprised if tap water needed any further purification, assuming that the mains water you have is treated as it is here in England.
Isn't it strange how there was a big fuss over Dasani in the UK yet we're happily drinking River Rock which is produced by the same people in the same way - symptomatic of how we deal with things here.