It’s important to keep indoor humidity at an optimum level (45 to 65 percent). Dry air in the winter  is one the main causes of sinus infections and sore throats. You can use a mechanical humidifier to add moisture to the air, but these devices require constant cleaning to prevent the growth of microorganisms.

An easier way to add humidity to a room, is to put a few areca palms in it. These palms release copious amounts of water into the air, and remove chemical toxins too. They are consistently rated among the best houseplants for removing all indoor toxins tested. According to B. C. Wolverton, author of How To Grow Fresh Air, a six foot (1.8 m) areca palm transpires approximately 1 quart (1 litre) of water every 24 hours. So if you put three in your bedroom, the palms will be release three quarts of water per day — not bad!

Energy Consumption: 18 or 24W DC
Dimensions: 12" H x 12" L x 9"
Weight: 2 lbs.
Best Price: $202 (Alternative Energy Store) or $259 (Southwest
Solar)

Notes from Manufacturer:
World’s lowest energy using cooler. Evaporative cooling for RVs, boats, cars,
tents and small rooms at a fraction of typical air conditioning energy costs.
Cools hot dry air as much as 35 degrees F. Connect to DC battery, cigarette
lighter receptacle, or solar module. Lightweight and portable-use for camping
and backpacking. Doubles as a good humidifier. 200 CFM. Uses 1 to 1-1/2
quarts of water per hour. Warranty: 5 years on highest efficiency CelDek(tm)
pad, 1 year on everything else.