Water solutions

I’m after advice from experts on getting water while out hiking… I drink like a horse on hikes and managed to go through 4 litres in my backpack in about 4 hours this, and last hour back to the car was dire (water also shared with my dog, I probably drank 3/3.5)

I don’t really want to carry any additional water for weight and space so that leads my to the solution of water filters

I’m not too fussed on recommendations for brands (I can research that another time) but how in this country to I use them?

We hiked Waun Fach at the weekend and the only water available was lower down the mountain, and the highest point where the water was enough to collect, there was a dead sheep in it.

So anything further down would have had that in right?

Or by the time I get to the faster flowing river is it so diluted it would be ok?

Or can I just collect water from the reservoir that was there?

Do you boil then filter? Or filter then chlorine treatments?

I can’t seem to get to the bottom of these questions anywhere

Thank you in advance!