If you don't add water or if the water in the humidifier runs out, the machine will still deliver pressurized air, but the air will not carry added moisture. Humidification itself is not essential to the effectiveness of CPAP therapy, but it can be important to addressing dryness in the nose or mouth.

If you forget to put water in your CPAP machine's humidifier chamber, you will likely wake up with a severely dry mouth, raw nasal passages, and a sore throat. The machine will continue to provide the necessary air pressure for your sleep apnea therapy, but without the moisture, the air becomes incredibly dry as it passes through the heated tubing. Many users in 2026 report a "traumatizing" burning or melting plastic smell if the heating plate continues to run with an empty tank, which can leave a lingering "burnt purple" taste in the nose for days. Physically, the lack of humidification can lead to "nasopharyngeal dryness," which can eventually cause sinus infections or nosebleeds if done repeatedly. While it generally won't "break" the machine itself, modern devices often have a "Humidifier Off" setting that you should engage if you plan to sleep without water. To avoid this, many patients now use automatic replenishing systems like the CSpring Mini, which ensures the chamber never runs dry, preventing the discomfort and the dreaded odor of a dry heating element.