WH's are a tropical plant, and can't take cold weather. They're also very heavy feeders.
What a lot of people do (assuming you don't' want to pollute the pond just to make the WHs happy) is to put some dried cow or chicken manure (find it at a garden store) or worm casings into a bucket or tub. Add water, and put some of the WH's in for a few days.
I have never managed to keep WH alive indoors over the winter.