To solve this problem, we need to understand the concept of water potential.$\newline$Water potential (\Psi) is a measure of the potential energy of water in a system compared to pure water, where the water potential is zero.$\newline$It determines the direction of movement of water.$\newline \bullet$In pure water, there are no solutes, and the water potential is at its maximum value.$\newline \bullet$By definition, the water potential of pure water at standard conditions (temperature and pressure) is zero.$\newline$Therefore, the correct answer is Option 4: Zero.