How clean is it? Well if you don't test it in some way you really don't know.
If someone in the house likes to drink distilled water directly from the jug. Then it might not be sanitary anymore.
But for the most part, I'd trust it to be clean and sanitary up until the day that I got a infection and was able to determine it was the water. Though that might be hard to prove definitively. Unless I still have the jug of water and tested it.
If you don't want to take the risk, then just boil it the day before and let it cool with the lid on. But for the most part, bottled water of any sort should be clean and sanitary. But mistakes happen!
Especially if someone in the house likes to drink distilled water directly from the jug.