I informed our readers recently that it's a good idea just to toss a little bleach into your vases of cut flowers.
Here's another tip (also via Mrs. BD's garden club). When you force Paperwhite bulbs, always throw in a shot or two of vodka or gin into their water once they sprout up a few inches. It stunts their growth just enough to prevent them from getting leggy and falling over. It has no impact on the bloom - or the scent.
One might like to imagine that it cheers them up, too. Grey Goose, of course.
Here's a reference on the topic.