The white powder build-up you see in/on your humidifier is the result of minerals in your tap water, otherwise known as hard water. Clean the nebulizer and water sensor with a soft cloth and a small amount of undiluted white vinegar. If necessary, mix a solution of 50% white vinegar and 50% water and fill the base with enough solution to cover the nebulizer. Allow it to soak for an hour and then use a cotton swab to gently loosen buildup on the nebulizer. Rinse the base with clean water and wipe with a soft cloth. To keep it from building up, please use distilled water in your humidifier.