There are formulas for working out how much water you need but you need to calibrate this against your system.
Working backwards In total you want:
Batch = say 23L into the FV
Kettle waste = say 1L (you'll want to confirm this for your kit)
Boil off = 4L approx (you'll want to confirm this for your kit)
Grain Absorbs = roughly 1L/KG
So assuming a 5KG malt bill you'll want 23+1+4+5 so 33L total.
This wants to be split between the Mash and Sparge so assume mash volume of 2.5L/KG to 3L/KG.
So 15 Litres to mash in and 18 Litres to Sparge with.
This is just a guideline and as you do more you'll get an idea what you need to hit your numbers.
Working backwards In total you want:
Batch = say 23L into the FV
Kettle waste = say 1L (you'll want to confirm this for your kit)
Boil off = 4L approx (you'll want to confirm this for your kit)
Grain Absorbs = roughly 1L/KG
So assuming a 5KG malt bill you'll want 23+1+4+5 so 33L total.
This wants to be split between the Mash and Sparge so assume mash volume of 2.5L/KG to 3L/KG.
So 15 Litres to mash in and 18 Litres to Sparge with.
This is just a guideline and as you do more you'll get an idea what you need to hit your numbers.