Spare charcoal kicking around in the barbecue? Set aside a few briquettes to keep flowers fresh around your home.
You've probably noticed that the water in a flower vase starts to get stale and dirty after a few days. If you don't want to deal with frequently replacing the water, placing a small lump of charcoal at the bottom of the container will help it stay fresh longer, which can keep your flowers from wilting for a few extra days, and at the very least will keep the water from looking as gross.
You've probably heard of charcoal filters for fish tanks or Brita filters, and this basically applies the same concept to a flower vase. For more clever uses for charcoal briquettes, check out the source link.