Final answer:
Water helps clear the tube so it doesn't get clogged.
Step-by-step explanation:
The nurse should respond to the client's question by saying, "Water helps clear the tube so it doesn't get clogged." Adding water after the formula drains from the syringe helps to flush out any remaining formula and prevent the tube from becoming clogged. This is important for maintaining the patency and functionality of the NG tube. It is not necessary for making sure the tube stays in place, providing enough fluids, or making the formula less concentrated.