Method and a system for estimating the water content of brake fluid in a brake system

A brake system for a vehicle, the brake system comprising:

• a plurality of brake calipers;
• a brake fluid container comprising a sensor configured to detect a parameter indicative of a water content of the brake fluid in the brake fluid container;
• and
• a control unit configured to determine a water content of brake fluid in the brake fluid container based on the detected parameter and to estimate a water content of the brake fluid in a brake caliper based on the determined water content of brake fluid in the brake fluid container using a predetermined model describing the relation between the water content of brake fluid in a brake caliper and the water content in the brake fluid of the brake fluid container;
• wherein the predetermined model is established based on a determined water content as a function of time by:
• arranging the brake system in a controlled environment;
• for a predetermined time period, exposing the brake system to a controlled air temperature and air humidity for a predetermined period of time such that an increase in water content in the brake fluid is accelerated in comparison to an increase in water content during normal operating conditions of the vehicle;
• and
• determining the water content of the brake fluid in the brake fluid container and in each brake caliper as a function of time during the predetermined time period.