Plan to water your tillandsia with a couple of methods used in concert. Although rain water is best,  tap water is usually fine for air plants, as is well water. Do not use distilled water or softened water. If you are using tap water, set a bowl of water on the counter for a few hours prior to using it for your plants. This way, the chlorine can evaporate before you add the air plants. Submerge your air plants in the water, and leave them soaking for an hour. After their bath, gently shake the excess water from the plants and set them out in good air circulation to air dry upside down, to let all the trapped water run out and dry. Check the plants after four hours. If they are fully dry, return them to their display. It is important not to let the plants remain wet, or they will rot.