A dehumidifier is mostly a household appliance that reduces the level of humidity in the air, usually for health reasons, as humid air can cause mold and mildew to grow inside homes, which has various health risks. Relative humidity is preferably 30 to 50%.[1] Very high humidity levels are also unpleasant for human beings, can cause condensation and can make it hard to dry laundry or sleep. Higher humidity is also preferred by most insects, including clothes moths, fleas and cockroaches. Dehumidifiers are used in industrial climatic chambers for keeping certain level of humidity.

Most dehumidifiers can be adapted to connect the drip output directly to a drain via a garden hose, though they usually also come with a collection receptacle. There are usually sensors to detect when the collection device is full, and shut off the dehumidifier. These buckets will generally fill with water in 8-12 hours and will need to be emptied and replaced. Some dehumidifiers can tie into plumbing or use a water pump to drain themselves as they collect moisture.