Ah, cattails. Used to see them all over the place here while I was growing up. Can't say I have for a while now.
My suggestion would be to make cattail tea. Don't pick them when they're green. They need to brown and on the drying side. But not to the furball point. Then, instead of drinking it hot, drink it ice cold. Put in a lot of sugar, or sweetener of your choice, and then put the pitcher of cat tail tea in the coldest part of your refrigerator. Wait about 24 hours.
You could add cinnamon to taste. Add eat some watermelon with it.
DISCLAIMER: I have no idea what I'm talking about when it comes to cattail tea. Listen to me at your own risk. Any bodily functions which cease to function or reduce in function or function in ways they weren't meant to function due to following my rather silly suggestion is solely your fault. It would be better if you just forgot what you read above this disclaimer. Don't forget the disclaimer, though. That you need to remember.
You could follow this link, though, if you want a little herbal history of cattails and their potential uses.
Antiseptic, good for nosebleeds and other types of bleeding, poultice, shrinking cancerous tumors, poison absorption, particularly arsenic. Don't ingest if pregnant.
I wonder if it's any good for sunburns?
That's pretty cool about the arsenic...