Your questions really can't be answered with specifics without knowing more about the layout of your neighborhood and that level of detail is something that really shouldn't be shared on these forums, anyhow, being publically visible. That said, if you want to split into two teams, each with the own base, but be fair, you can set up a game in which neither team can use the hose for refilling during the game. Instead, each team has an equal number of water bottles/buckets/some other way of refilling that's available. The location of the other base really depends on what properties/areas you can access without trespassing on private property or causing concern with other neighbors. I've had water blaster fights in neighborhoods I was not as familiar with, but the local kids were invited and joined in (with parental permission) and thus we had a lot of areas which opened up by doing some brief chatting before we actually started (~15 mins of prep time). It is amazing how accommodating some can be if they feel they are being respected and informed of what you are planning (i.e. holding a water war in the area). Of course, I've also had to deal with people who didn't want us battling anywhere near their property; thus, some areas got flagged as "illegal areas" and Players were forbidden from going within water blaster firing range of these properties (to even avoid the chance of a mis-fire straying onto private property).
