A normal blood pressure reading should be lower than 120/80. That being said, I agree with the previous comment that 48 is on the low side and recommend consulting withe your MD to make sure there are no underlying issues causing a lower than normal diastolic blood pressure. Most likely simple dehydration is the root of the problem, but still worth checking out.
Here is a good article that offers several possible reasons for a low blood pressure - Can Blood Pressure Be Too Low?
All the best,
Lisa Nelson, RD, LN
Tips to Control High Blood Pressure
48 is pretty low. Being low is just as bad as being too high