You also have some other problems.
1. Look at your CPU usage. You need to add some time delays or move to an event structure (The event structure would remove your continuous DAQ writes). Sitting idle, your VI runs at 50% CPU on my system, and then shoots up to 75% when I turn the water on.
2. Your logic is also assuming the user never turns the water back on after turning it off. If you turn it off, wait 10s, then turn it back on, you'll notice your elapsed timer jumps 10s because it was never reset, so your final number will be inaccurate.