Please check online which type is advised in your system. It’s either dot 4 or 5.1.
As brakefluid contains chemicals that naturally atract water, it’s advised to change your brakefuild once a year.
there are two main reasons for that.
The first one, obviously, is that water in the system is not good for your components. There are a lot of tiny parts in your brake system and they do not like water at all. The second reason is the compression rate of water and the boiling temperture. Brakefluid is made from chemicals that do not compress much. That way, you can transport the pressure from the lever to the caliper. With a line full of water you’d just compress the water and have no pressure. Furthermore, water boils at 100 degrees celcius and brakes can get much hotter then that. Water above 100 degrees celcius is steam and well… we don’t need to explain how that effects your braking power do we?