washer fluid metering

I was very surprised when I discovered that I don't have a low washer fluid indicator in my Taurus 2002. I've one in my Windstar 98.
The question may be dumb, but how can I know how much washer fluid I have and know when I'm running low? Because the reservoir is hidden inside under a metal wall.
I don't have a gauge either.

So I just need to add on a regular basis?

In Toyota for example, there are a red polystyrene floating gauge in the reservoir. When it disappears, we know that we need to add fluid.

Yep, before heading out on a trip, when you check your tire pressures and other fluid levels, top off the washer solvent. Just don't pour it in too fast as by the time you see it, it will get to the top pretty quickly.

-Rod

In cold weather, we use it a lot to defrost the ice, ever for daily 2 miles trip. I should add each week.
BTW, I just discovered that the washer fluid in Taurus in heated to defrost ice more efficiently by engine coolant. There's an antifreeze metal hose that pass very close to the washer reservoir.