There is a water fountain by the church in Lago, 5 KM after Montefurado. So, not as far as Berducedo, a bit better.
Unless you stay in Samblismo, which is the last place before the Hospitales, there is vending machine in Borres (good for those starting out further back from Campiello).
So from Borres to Lago will be 21 KM.
You’ll know from walking the previous 3-4 days how you consume water in this Camino, as weather, elevation etc will make it probably different than what you’re used to.
For this stage I topped up my bladder so had 2L (usually I only partly fill it), plus a 500ml lifestraw bottle.
I walked in October and although it started off a cool morning, by the time I reached Montefurado it was proper hot. I had to start thinking of rationing my bladder, and reached Lago just when I was down to the last drops of the bladder but with the 500ml bottle still largely intact - I drank from it when having lunch.
FYI, the man who lives in Montefurado doesn’t like pilgrims using his external tap, even when they ask for permission they will get denied and with strong words. I think it’s such a shame, he will be very popular if he installed a vending machine there! Or a food truck in Puerto del Palo.