To compare a group of patients with our standard treatment of continuous positive airway pressure (CPAP) and another group of patients with CPAP and a humidifier attached. The therapy cost and the successfulness of the treatment will be measured. A humidifier is a water chamber that is currently added to CPAP only if the patients needs it.

Inclusion Criteria:

• Older than 18 years of age
• Diagnosed with OSA (obstructive sleep apnea) and eligible for CPAP treatment under local requirements (NICE guidelines: AHI (apnea hypopnea index) ≥ 15, or AHI > 5 with significant daytime sleepiness)
• Naïve to CPAP therapy, i.e. have not been prescribed, or used CPAP in the last 5 years.
• Fluent in spoken and written English

Exclusion Criteria:

• Significant uncontrolled cardiac disease, as per the principal investigator's discretion
• Co-existing lung disease, as per the principal investigator's discretion
• Co-existing sleep disorder, such a predominant central sleep apnoea
• Pregnancy
• Participants that are unable or unwilling to give informed consent.