How you can stop reverse rotation of cw pump?

Are you sure it's pumping in the wrong direction? It should be pulling water from the radiator through it's lower hose. Water will be returning to the radiator through the upper hose past the thermostat after it warms up. If your water is flowing the wrong direction and you have a mechanical pump ( one with a belt on it ) you will have to replace it. If you have a uni-belt setup (serpentine belt), it may be on incorrectly. If you have an electrical water pump ( probably aftermarket ) reverse the polarity on the power connection.