Use appropriate fluids. If there was a cheap alternative which was just as good, do you think that the commercial brands would still be in production?
Heat them correctly (some small operators use commercial urns of the kind that char ladies used to boil water for tea in - quite effective). This makes a huge difference.
Do not abuse the fluids and I’m sure you know NEVER to fly with ice on the aircraft.
A decent winter ops course might be a very good investment.
Where are you based?