1996 Ford Taurus brake fluid

I just acquired this vehicle yesterday and the brake fluid was bone dry, I put one container in and drove for a while, then the brake light came on and I pulled over and had to put another container in. I took it home and as it sat overnight it was fine it did not leak any brake fluid so does the car have to be in use for the brake fluid to leak or dissipate or is it normal for it to take one or more containers to replenish the brakes lubrication