Toilet leaks can be wasteful and expensive. At least once a year, check your toilet for leaks by adding a small amount of red food coloring to the tank, and then check the toilet bowl later. If the toilet bowl water is colored red, water is seeping through from the tank. If it is leaking, you should replace the tank ball.
Check the emergency shutoff under your sink to make sure it's fully open. If rubber washers or seals have begun to deteriorate, you'll also lose water pressure, so check those. Calcium and lime buildup will also cause low water pressure.