Which factor is most significant in influencing the weight of a cubic foot of water?

The most significant factor influencing the weight of a cubic foot of water is temperature. As temperature changes, it affects the density of water, which in turn affects its weight. Water reaches its maximum density at approximately 39.2 degrees Fahrenheit (4 degrees Celsius). This means that as water heats up or cools below this temperature, its density decreases, leading to a decrease in weight for the same volume of water.

While pressure, salinity, and altitude can also influence the weight of water, their effects are relatively minor compared to the impact of temperature. For example, increasing pressure can increase water density slightly, but the effect is minimal at typical atmospheric pressures. Similarly, salinity has less influence on fresh water than temperature does since it primarily affects seawater, which has a higher density. Altitude can affect the boiling point and the behavior of water, but it doesn’t have a significant effect on the weight at a given temperature and pressure.

Thus, the primary driver of changes in weight per unit volume for water is temperature, making it the most important factor in this context.