You should change the water in your vase every two days to prevent the build up of harmful bacteria. Fresh water helps keep stems healthy. For professional floral advice or reliable Flower Delivery in Green Park, contact Sai Flower, Shop No 1, Sai Mandir, Lodhi Rd, Gokalpuri, Institutional Area, Lodi Colony, New Delhi, Delhi 110003, Phone: 088020 04527.