The density of the flume water was measured in the same temperature range. It was found that the difference between distilled water and flume water density has weak temperature dependence (Figure 19).
The density of the flume water can be found by adding an additional linear term
430.33213.63110,/Tkgmρ−Δ=−⋅ ,
to the distilled water polynomial (where T is in °C) . The maximum uncertainty for the density difference is about 0.004 kg/m3 which is negligible compared to the uncertainty (0.05 kg/m3) for the 4 fluids previously described. . The expanded uncertainty is about 100 parts in 106. The density of the flume water is checked once a month or after adding water to the reservoir.