I worked for a while at an office and lab at the top of Portsdown Hill, Portsmouth. The water pressure up there was too low to use for fire fighting, or the main was too small, I'm not sure which, but the solution was to build large ornamental ponds at the front of the building that doubled up as a source of water for fire fighting. Something similar was done at another place I worked at for a time, Abbey Wood, near Bristol. There the large ponds also acted as storm water run off storage, as well as providing water for fire fighting. I think it's a fairly common commercial solution to this problem, so it should work OK for a domestic situation. 10,000 litres isn't massive for a pond, and could be pretty easily created with a digger and pond liner.