I bought a new fridge and moved the old one to the basement. Do I need to connect water supply to the old fridge to stop contamination of the lines, and water filter, by bacteria? I don't need the ice or water down there, but I don't want to damage the units either.
Once the supply lines for the fridge have had all the water evaporated there won't an environment for mold to grow. The same can be said for bacteria.
You may be able to facilitate the evaporation by opening the hose somewhere in the water supply line which would allow the water to drain faster. If there is a disposable filter it should be removed as it will be difficult to remove all water from it's filter medium.
Once the water is removed a plug inserted at the open hose end or crimping it with tape will seal the water system.
If and/or when it is attached to a water source flushing the line is a wise idea. And a new filter will keep contaminants out.