Bring the water (or stock if you prefer) to a low simmer. You never want the water to come to a full boil, so control the heat. If using fresh peas, blanch them in the simmering water for about two minutes. If using frozen peas, pop them into the microwave for 30 seconds to thaw.
Grate the parmesan cheese on the small holes of a box grater. Use a microplane grater to zest the lemon, then juice it.
Cut the bottom roots and the dark green tops off the leeks, then slice them in half. Run them under cold water until clean. Slice the leeks into thin ribbons with a sharp knife.
Melt the butter in a wide deep skillet or Dutch oven over medium low heat. Add the leeks and a pinch of kosher salt. Cook until they are soft and translucent, 5-8 minutes. You don't want them to brown.
Turn the heat up to medium, add the rice to the pan, stir to coat with the butter, and toast it for about 1 minute. Add the white wine and stir until it evaporates.
Add about 1 cup of the water to the pan along with the parmesan rind if using and stir frequently, but not constantly. Stir it gently every 30 seconds or so, making sure it's not sticking to the pan. (I like to use a wooden spoon.) Be sure it's bubbling at a medium simmer, if not, adjust the heat accordingly. When that liquid has absorbed, add another cup of liquid and repeat until the rice is al dente. It should take between 16-20 minutes if you've got your cooking liquid and your pan of risotto at the right temperature.
You'll know the risotto is finished when most but NOT all of the liquid has been absorbed, and the rice has a chewy al dente texture. Turn off the heat and let it sit for about 2 minutes.
Stir in the salt, lemon juice and ¾ of your lemon zest. Add the parmesan and peas to the risotto, stirring vigorously to create a creamy sauce. Taste for seasoning and add more salt if necessary. Top with remaining lemon zest and freshly ground black pepper.