Method and an apparatus for evaluating a condition of a water purification system

A water purification apparatus arranged to output purified water through an outlet port and through at least one sterilizing grade filter of a line set fluidly connected to the outlet port, the water purification apparatus comprising a control unit configured to:

• monitor, by means of a flow rate sensor that is located fluidly upstream from the at least one sterilizing grade filter, a flow rate that is correlated with a flow rate of the purified water flowing through the at least one sterilizing grade filter;
• monitor, by means of a pressure sensor that is located fluidly upstream from the at least one sterilizing grade filter, a pressure that is correlated with a pressure of the purified water flowing to the at least one sterilizing grade filter;
• and
• evaluate a condition of the water purification apparatus and/or the at least one sterilizing grade filter based on whether a relationship between the monitored flow rate and the monitored pressure exceeds one or more limits indicating one or more system dysfunction criteria is fulfilled, wherein the relationship is:
• (i) a ratio of the monitored flow rate to the monitored pressure, wherein:
• a first system dysfunction criteria of the one or more system dysfunction criteria is fulfilled when the ratio exceeds an upper ratio limit of at least 3,
• fulfillment of the first system dysfunction criteria indicating that the at least one sterilizing grade filter leaks, and
• a second system dysfunction criteria of the one or more system dysfunction criteria is fulfilled when the ratio falls below a lower ratio limit of at least 0.5,
• fulfillment of the second system dysfunction criteria indicating that the at least one sterilizing grade filter is clogged and a bioburden of the water purification apparatus is too large, or
• (ii) a slope value of a curve of a function of a ratio of the monitored flow rate to the monitored pressure versus time, wherein the slope value extending beyond one or more slope limit values indicates another system dysfunction criteria of the one or more system dysfunction criteria is fulfilled.