Open the hood of your Mazda5 by pulling the hood release under the dash. This will allow you to access the washer fluid reservoir.
The washer fluid reservoir on a Mazda 5 is white/translucent and has a wiper symbol on top. If your Mazda5 has a rear wiper, it is feed by the same reservoir according to Mazda 5 owners manual.
Open the washer reservoir cap.
Add washer fluid until the level gets about two inches below the reservoir cap.
Do not use engine coolant antifreeze to mix or make windshield washer fluid. Note that on Mazda5, both front and rear wipers use the same washer fluid reservoir.