Using a sharp knife or a channel knife, remove the zest from all the lemons. Split in half and set aside then cut the lemons open and juice the lemons. Split the juice in half and set aside.
In a small saucepan over medium low heat, add in the sugar, water, one half of the lemon zest and one half of the lemon juice*. Bring to a simmer, let simmer for five minutes then turn it off.
Add in the second half of the zest and juice and a pinch of salt. Allow to set until the simple syrup is completely cooled. Use a fine mesh strainer to strain out the pulp and zest from the syrup then store for up to a month in the refrigerator.
Notes
*Avoid stirring as much as possible. This heightens the chance that the sugar will splash onto the sides and become difficult to clean. The bubbles from the simmering will do most of the stirring work for you.