An in-toilet leak detector is disclosed, as are communication systems for reporting toilet leaks. The leak detector comprises an inlet that receives water from the toilet's fill tube and diverts it through a flow tube. A capacitive sensor is located between the inlet and an opening of the flow tube from which water flows into the overflow tube of the toilet tank. A housing is connected to the flow tube and the inlet and contains a controller and other electronics, including one or more transceivers. The leak detector measures the duration of water flow and establishes an alert if the water flow is shorter or longer in duration than a calibrated normal duration. The transceivers connect the leak detector to a computer network, and leak alerts are communicated to a server or servers so that they can be forwarded directly to those responsible for fixing the toilets.