the resistance is low and if there is no water the resistance is high therefore the sensor unit 30 determines if there is water flow or not the sensor unit 30 senses the trapped water and determines how long the trapped water has been stagnant in the trap if the water is not flowing then the trapped water is considered to be stagnant and a timer times the stagnation time if the water is flowing then there is no need for ionization since water is not stagnant the sensor unit 30 is connected to the control system 70 by wires 31 to determine the ionization period other types of sensors such as conductive and capacitive level sensors hydrostatic pressure level sensors acoustic laser and can also be used for instance a conductive level sensor suitable for conductive liquids such as water can be used as a sensor such sensors comprise of stainless steel plates having a ceramic polyethylene or teflon based isolators between them conductive sensors use low voltages and currents and have the additional benefit of being solid state devices and are very simple to install and use as shown in fig3 a e and 4 a e another embodiment of the present invention can have a different design for a siphon trap disinfection unit which provides a constant sterilizing of siphon trap by using the ionization chamber and the copper wire the siphon trap in the present invention as shown in fig3 a e and 4 a e can have varieties of designs the siphon trap can.