We just installed new thermostats on our electric water heater, but the breaker keeps throwing, My question is at the breaker box, is the black wire on top or bottom when hooking up a new breaker, and at the water heater is the black wire on the left or right on the thermostat? My wire colors are white and black.

Does not matter when using 240 volts which wire is which, technically the white needs to be relabeled as hot in the latest code, to indicate both are hot.

Disconnect the feed wires at the heater, cap, and reset the CB,if it trips the short is in the feeder, if reconnecting trips the CB the short is in the heater, and if nothing is obvious, like a cut wire digging into metal, or a short at the connection, must be a miswire. For that a wiring diagram is needed to find the improper connection.

Does the breaker trip instantly, or does it trip after a few seconds? A short will trip it instantly.