I used spent espresso coffee grinds to pH Down my water. What would happen if I used it?

Hi there.. I am growing cannabis but this is actually just a general question as it's kind of possibly ridiculous in theory and I have found absolutely NO mention of such things via Google at this time. I grow indoors, and in Black Swallow soil: KIS Mix Blended Soil | Black Swallow Living Soils, Brantford ON (blackswallowsoil.com)
However our tap water here in Waterloo region is outrageously hard, and outrageously high in pH (8.2 at times!).

Here is our water breakdown:



We make minimum 2-4 espresso per day in our house between me and the wife. I heard coffee is acidic so just for fun I stuck my pH pen in a litre of water and added already brewed leftover grinds to bring the water from 8.1 to 6.5. It worked, quite well!

Then I ran the concoction through a chemex filter to remove all of the actual solids

And I am left with a brown transparent liquid with a pH of 6.5



What would happen if I dumped it on a plant in veg? Or used it as a starter liquid to a quick castings tea for example?

I’m assuming it has some nitrogen but doubt it would be enough to be instant toxic. Or would I be wrong?

I didn’t feed anything lol but I have too many plants in veg right now, maybe I should sacrifice one as a test dummy

And as a reminder, this is already brewed leftovers that would otherwise be thrown out so I am keen to know if there’s anything I can do with it (I don’t compost sadly, no room at the moment)