What is the primary danger of operating a vehicle with brake fluid that has absorbed more than 3% water?

1. The brake lines will freeze solid in normal tropical weather
2. The water content lowers the boiling point of the fluid, which can cause 'vapor lock' and sudden pedal loss under heavy braking
3. The fluid will turn into an acid that eats through the brass caliper fittings within a week
4. The ABS pump will run backwards, reversing the brake operation