I always time my pure water production. 20 minutes for every 100L to be made. I needed 300L to fill my IBC tank today. So the timer was set for 1 hour. Timer went off but I got way laid and went out to the garage a couple of minutes later to find it was still running and it was overflowing out of the lid. The auto shut off valve had failed! The first time in a long while it had done so. Imagine if I'd left it on over night?