$900 in a month is about $30 a day which is an average load of from 6 to 12 KW depending on the local power price, perhaps 5KW if power very expensive.
A large low efficiency air conditioner could certainly use say 4KW, which with a few other loads might reach 6KW, together with a high power price, this could explain the bill.
And remember that a "month" can be as long as 45 days depending on meter reading dates, public holidays etc.
As posted above, it is unlikely that a fault would waste that much power without something catching fire or blowing up.
A leak of hot water could do it though, resulting in the water heater running 12 hours a day (it is stated to be turned off for half the day)
If the premises have been empty for a while, then the bill may include months of standing charges, or some small load left on for months, before the present customer moved in.
Or even money owed by a previous customer.
Or as posted by others, the utility may have mis read the meter or read the wrong meter.
