When buying irises, buy them at the bud stage. Irises open very quickly, and getting them in bud will give you maximum enjoyment from them. Change the water in your flowers every other day, or when it looks cloudy. Always remove leaves that will be below the water line. This keeps the bacteria down and helps the water stay clean longer.
Flowers appreciate being spritzed with water often.
Also, keep the water level in the container at a consistently high level to keep flowers fresh longer.