What should be monitored when checking the weight of water?

When checking the weight of water, monitoring the temperature is crucial because the density of water can vary with temperature changes. Water is most dense at about 4°C, which means that its weight will differ slightly at different temperatures. This is important for calculations that involve water weight, such as determining the amount of water needed for firefighting operations or assessing water supply systems. Understanding the temperature at which the measurement is taken allows for more accurate conversion between volume and weight, which is essential for effective planning and response in fire operations.

The other options do not directly impact the weight of water. Humidity affects air moisture content but not the weight of the water itself. Pressure can influence the water's state, especially in pressurized systems, but it does not alter the actual weight of water. Flow rate is important for understanding how fast water is delivered but does not provide information about the weight of the water being measured.