Answer:
potential to kinetic energy
Explanation:
Water kept in a water tower posses potential energy by the virtue of height of tower.
When this water starts draining from the tower, the static water gains velocity and starts flowing. The water starts flowing after the potential energy in it converts into kinetic energy.
Potential energy is equal to 
Where m is the mass of water
g is gravitational constant and
h is the height (of the water tower) at which the water is stored
While kinetic energy is equal to 
where v is the velocity with which this water flows
Hence, the energy conversion depicted in this case is from potential to kinetic energy