6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

On the left side of the equation, we have:

* 6H₂O

Each water molecule (H₂O) contains 2 hydrogen atoms.

Therefore, there are a total of 6 x 2 = 12 hydrogen atoms on the left side of the photosynthesis equation.