People use humidifiers for different reasons: to prevent dry skin, keep tropical houseplants healthy, improve allergies or sinus problems, and increase home heating. No matter the reason for use, all humidifiers need regular maintenance and care. Following the manufacturer's instructions is the easiest way to ensure your health is safeguarded and the machine keeps working. Most manufacturers instruct consumers to use filtered or distilled water. Not following this directive can have some potentially harmful results.

Consumer Reports outlines three basic types of humidifiers. Tabletop humidifiers have small tanks with enough space to hold water to humidify one room. Console humidifiers are larger than tabletop humidifiers and store enough water to humidify more than one room. In-duct humidifiers service a whole house via a forced-air heating system. Humidifiers are also present in some medical equipment, such as CPAP machines. Humidifiers may be evaporative, warm-mist or ultrasonic nebulizer-type humidifiers. Evaporative humidifiers blow air over a wet wick, warm mist and impeller types boil water, and ultrasonic nebulizers utilize high-frequency sound waves to create moisture.

Humidifiers introduce warm moisture into a room for the purpose of improving atmospheric moisture. Manufacturers recommend using filtered, distilled water to prevent the buildup of microorganisms in the environment and prevent mineral scale buildup on the machines. Some individuals using humidifiers may observe white powdery buildup on surfaces near humidifiers run with tap water. Despite most manufacturers' recommendations, the Environmental Protection Agency notes the government has not concluded that there are any serious health risks posed by using regular tap water in humidifiers.

Humidifiers are run when people are home and in the area occupied by the humidifier. This makes the prevention of potentially harmful microorganism spread imperative. W. Steven Pray, author of the pharmacy textbook "Nonprescription Product Therapeutics," advises that, while the steam produced by humidifiers is sterile, these microscopic threats are carried on water droplets emitted by impeller-style humidifiers. Pray describes an illness known as "humidifier fever." Symptoms include respiratory difficulty, coughing, fever, fatigue, body aches, tightness in the chest, unexplained weight loss and headaches. Symptoms subside when the humidifier is removed, but recur upon reintroduction of the unit.

Although the exact cause of "humidifier fever" is unknown, it is ascribed to an allergic reaction rather than an infectious substance. Pray also states an increase in asthma among humidifier users, though a concrete reason has not been identified. The use of filtered water may alleviate some of these issues.

Filtered water alone isn't enough to prevent microorganism growth in humidifiers. In addition to using proper water, regular cleaning can remove potentially harmful microorganisms from the humidifier and prevent those microorganisms from spewing into the air. The Environmental Protection agency notes distilled water is the safest and most effective at preventing buildup on machines. Deionization and reverse osmosis are less effective than distillation but still contain fewer harmful substances than untreated tap or well water. The EPA advises consumers to check water labels. Water marked “spring,” “artesian” and “mineral” may have been filtered to remove pathogens, though the water still contains minerals that can harm the machine. Filtration and demineralization cartridges and supplies are available for use with some humidifiers.

The New York Times offers food for thought, stating that about 90 percent of the substances dissolved in your water will make it into the air you breathe. That includes bacteria, viruses, fungi and organic matter. Those particulates are incredibly small and are easier able to invade your lungs. Adding bleach or disinfectants to humidifier water does not get rid of them -- these substances can contribute to an allergic reaction in some individuals.