I'm not rying to tell you what to do, I just never understand why people want to drop $1000 in tanks and equipment, $500 in livestock, Etc. but they don't want to spend $100 on a quality water source. There are always exceptions and I understand that. Can I ask why your "mate" is charging so much? Is water that expensive in the UK? Is it to help cover filter changes? If you guys have good tap water filters over there you could use that for the initial fill but from my experiences with our units and there prices the proper filters cost just as much as a RO unit. If you have the patience you can use regular tap water initially. You just may have some earlier, heavier algea blooms. But if after the first fill you continuously use RO afterward it will clear with time