I do hope 'Still foaming' you are reading this as I stand corrected....ouch!!!.
I apologise but most water features I've seen are in the garden. However I now understand that there are indoor water features having seen one. I am very sorry but cannot give any advice as it seems a strange thing to happen.
The only indoor water feature before my recent sighting of the real thing was a leak in my kitchen tap feed.
All I can offer is check filters if there are any, if so and are suspect change them.
Charlie
May 2009