You can root stem cuttings of your pothos vine in water. Stem cuttings from many different plants will form roots when placed in water. In order to determine if the plant you want to propagate will respond to this method, you will have to consult several references. Not all plants will root in water, and roots that do form in water may not be well suited for transfer to soil. The best technique to ensure propagation success would be to take a stem cutting and root it in a sterile medium using a rooting hormone.