Replenish Your Flowers Water Frequently. Change All The Water Every 2-3 Days.

Flowers really do drink a lot of water! Large flower arrangements can suck up all the water in a vase within the first day or two from when you bring them home from the store. 

Make sure you keep the vase full of water so that the flowers don't dry out and wilt. Flowers are very susceptible to the bacteria that grows on the stems if they sit in water. 

Ideally you should change the water in the vase every few days, even if there is still some left, this will help keep your flowers fresh longer (and you won't get that horrid rotten smell that builds up if you let them sit too long).