Place the spinach and the water in a small saucepan over medium-high heat. Bring the water to a boil and cook, stirring continuously, until spinach is wilted. Pour the spinach mixture through a fine mesh strainer lined with cheese cloth. Retain the liquid. Gather up the cheesecloth to form a bundle and squeeze the excess moisture from the spinach into the reserved liquid.
Transfer the spinach to a food processor and blitz until a paste forms. Set the reserved steaming liquid and the spinach puree aside.
Whisk the salt and the flour together and pile it onto a counter in a mountain-like formation. Create a well in the center of the flour mixture and add the eggs followed by the spinach puree and the reserved steaming liquid.
Beat the eggs in the center, then begin pushing the dry ingredients into the wet until a loose dough forms. Using your hands, knead the excess flour into the dough until it is slightly tacky and silky to the touch. Wrap the dough in plastic wrap and let rest for 1 hour.
Divide the dough into quarters. Dust each quarter with cornstarch, then roll out the dough. Using a pasta roller, roll the dough out until 1/16 of an inch thick. I rolled my dough to setting number 4 on the Kitchen Aid Pasta Attachment. From here you can either cut the sheets of dough into noodles by hand or use a spaghetti cutter - I used the Kitchen Aid attachment.
Once cut, separate the individual noodles, then dust with additional cornstarch. Form the noodles into bundles and place them on a baking sheet dusted with cornstarch. Refrigerate until ready to use.