The present application generally relates to fluid flow detection apparatuses and methods for detecting a water leak in a pipe system of a building. A method may: determine that a low flow is present, if absolute values of temperature differences between ambient and pipe temperatures of respective samples of a first monitoring period are above a difference threshold; and perform a high flow test by estimating a temperature profile of water entering the pipe, based on identifying at least one temperature difference maximum of a second monitoring period, wherein each said difference maxima is a maximum temperature difference between ambient and pipe temperatures of a received sample, and determining that a high flow is present by detecting, based on the received pipe temperatures of the second monitoring period, if the pipe temperature is approaching the estimated water temperature profile.