How long will the Purest Sleep Diffuser run before it runs out of water? January 23, 2019 19:37 The Purest will last between 3-6 hours depending on the selected intensity level (low or high). Related articles Does the Purest Sleep Diffuser have timers? What is your return policy? My Hushh/Rohm/Travel Mini/Pocket Baby Soother will not turn on/off, and I have already made sure that the child lock is deactivated. How can I fix this? How does the sound of the Uno compare to the Dohm Classic? What is the energy usage for the sound machines?