Yes it can be charged in oil also.
You can consult the doctor if rubbing on spine is allowed. Or else just gently apply it.
Each method has its own convenience and approach….be it water intake or oil application.
Water intake reaches whole body. Oil may have a localised effect to that area.
You can do both also ….taking charged water and applying charged oil or cream. So in this way you increase the healing energy intake in simple ways.