All the details.

Brake fluid

Brake fluid mainly consists of the toxic and corrosive substance polyalkylene glycol ether together with special additives. It’s used to transfer pressure in hydraulic brake systems. To prevent the formation of vapour bubbles under high brake loads, its boiling point is very high (290°C). The fluid’s hygroscopic (i.e. water-attracting) properties require regular checks at prescribed maintenance intervals and a change of fluid if necessary. Even a small amount of water content lowers the boiling point significantly and may lead to the formation of bubbles that prevent applying full brake pressure. This would increase braking distances as a result.