The monitor window no longer seems to accurately handle water supplies. It shows how long the current supply of water would last with no recycling, regardless of whether or not the recycler(s) are running. Note: the recyclers still work, the monitor just isn't calculating the duration properly. The planner in the VAB performs the calculation properly.
Edit: it alternates between the expected duration and 'perpetual' depending on whether or not the recycler is running, due to waste water being generated all at once. My best guess is that when there is no waste water, the recycler doesn't run; then when the waste water is generated, the recycler starts running and the projection changes to 'perpetual' because water is being generated but not consumed.