Figure . Variation of the average transmembrane flux of water per minute, 𝐽 !,#$% , across time, as recorded throughout each BW30 preconditioning run. The dotted grey line highlights the stabilisation in gradient of 𝐽 !,#$% after 90 min. To yield an estimate of the steady state flux of water across BW30, 𝐽 !,#$%('') , the three preconditioning datasets were averaged to evaluate the variation of the mean average transmembrane flux of pure water per minute, 𝐽 ̅ !,#$% , across time). The results are shown in Figure , which reflects the reduction in 𝐽 ̅ !,#$% over time at a decreasing rate seen in Figure , with the gradient of 𝐽 ̅ !,#$% against time approaching zero after 90 minutes. Inspection of 𝐽 ̅ !,#$% and the associated error bars beyond 90 minutes of preconditioning suggests that the steady state flux of water across BW30 stabilises around 𝐽 !,#$%('') = 17 ∓ 2 𝑚𝑙 𝑚 )* 𝑠 )+ . Thus, for a conservative estimate, a value of 𝐽 !,#$%('') = 15 𝑚𝑙 𝑚 )* 𝑠 )+ may be assumed for the minimum expected steady state transmembrane flux of pure water. This result may be used to approximate the transmembrane flux of very dilute aqueous solutions, for which the BW30 transmembrane flux characteristics have not been determined experimentally.