Do you have suggestions for keeping water flowing at low-flow rates when the temperatures are -20 to -30 degrees?

This is one of the most difficult questions, but I have experienced working at -45 degrees.  When the flow rates are extremely low and the tubing diameter is small there is always a potential for freezing. One of the easiest solutions is to get some inexpensive pipe insulation and put it over your discharge tubing to retain enough heat from the groundwater itself in order to prevent freezing in the line. If you actually having freezing in the wellhead that becomes problematic. Using a slightly larger tubing diameter can actually help. If you are presently using ¼-inch tubing, try increasing it to 3/8-inch standard tubing. Using larger, insulated tubing may keep water flowing at the very low temperatures you describe.