Only put about 2 inches of water in your vase.
Then you can enjoy bouquets of fresh cut flowers for weeks.
That's enough water for the stems to drink.
People often fill their vases to within a few inches of the top.
Stems are not meant to be submerged.
I trim the stems at an angle every 2 or 3 days and change the water then.
As the stems get shorter, I move the flowers to another vase.
All my vases are clear plastic or clear glass so I can see the water level.
If your choice of flowers is more thirsty than mine - just top-up the water level to about 2 inches as needed inbetween the days that you trim the stems and give vase all fresh water.
I hope you get as much enjoyment out of your flowers as I do.