Brake fluid is relatively cheap and painless to change. If done annually the hydraulic components would last almost indefinitely. Use good D.O.T.4 brake fluid from sealed cans. If your car has French hydraulics, changing the fluid biannually is also a good idea. Use only genuine Citroen LHM fluid and keep some spare liters on hand, only a very few sell it.
Distilled water is cheap.
The average car takes about 2 gallons. Kettle stone will form on the inside of your radiator and engine cooling passages insulating them, causing your car to run hot. Eventually the deposits, mostly calcium, will push your radiator apart and make it leak. The battery should also only get distilled water. Mineral deposits inside your battery don't do it any good.