Toyota Repair: radiator problem?, toyota supra, left hand side

Question
I have a 1988 Toyota Supra.  Today a yellow light on the left hand side of the dashboard came on and remained constantly on.  The drawing that showed when the light came on looks like a cage.
I assume this is an indication of problems with the radiator.  Is there an additive I can put in immediately to take care of the problem until Monday when I can take the car to the shop?  Would it be okay to put in distilled water?  When I took off the lid of the radiator, I could see a green substance, so I didn't know if I could put in water (the only substance I have here at home).  Should I just not drive the car until Monday when I can take it in?  Your advise would be most appreciated!  Thanks.

Answer
Sorry, the answer may be a little too late, the sensor for the low coolant warning light is in the reservoir bottle, it looks like the engine is using some coolant either by an internal or external leak.
Yes you can add normal water from a hose, the green liquid is antifreeze.
Let me know if I can be of any more help.