It depends on the amount of grain you use. I use 3 or 3.5 Liters of water for 1 kg of malt. Example: Batch size on fermentor. 50 Liters. Boil Size: 60 Liters. ( I have 10 liters of losses during 60m of boil.) So: For 10 kg of malt, I use 30 liters for mash...