If the car is COLD, I would open the radiator, add water there and replace the cap. Do not do this when HOT, it will be under pressure. I would also add water to max in the bottle, and mark it with a pencil or something. Check often see if the level goes down. If it does, you can kinda guess the rate. An inch per hr? per 5 hr? This gives you an idea what you dealing with, and you can kinda expect how often you need to add water.
When I bought my SC430 several years ago, I notice I was losing coolant. Very slow leak but I can see the coolant level keep getting lower from my pencil mark at the bottle. I went thru the entire engine top to bottom, I can not figure out where it leaks. I replaced the cap and the leak stops. My thinking is that maybe the leak was so small that coolant would just evaporate. Cap is cheap, and I think it should be replaced as part of maintenance.
Echoing ^^. Water is for emergency, understanding that PO is far from home and with family in tow. Coolant should be used ideally, but when one is far away from home, trying to find an local Toyota dealer (or part store with Asian Zerex) is probably not easy task. I do think driving around with water for a bit will not hurt anything as long as it will be replaced with coolant later.
LC is build for service in third world countries, does anyone think they use the proper coolant, or distilled water there?
It could also be the mysterious leak many of us found below the heater ts at the bypass inlet/outlet.