When you receive roses you should always cut an inch off the stems at a slant. This enables the stem to take in as much water as possible. There are several suggestions of putting coins, bleach, lemonade, guinness, aspirins and the latest, even viagra tablets and probably many more obscure things in the water. My advice is simply to make sure your vase is spotlessly clean and if anything, a packet of flower food which any good florist will supply with your flowers. This helps to kill the bacteria in the water. If your roses do flop, then re cut the stems, roll in newspaper covering the heads so they stand up straight and dip the stems into a jug of boiled water for 30 seconds then plunge straight into your fresh, clean, cold vase of water and leave overnight. If the rose heads are not too past it this should help perk them up by morning. It helps release any airlocks in the stem.