Prepare the seafood:
Fresh clams have no fishy aroma but they do contain grit and sand. Scrub them under cool running water using a stiff kitchen brush. Place clams in a bowl and allow tap water to run over them for about 10 minutes. Lift the clams from the bowl and place in a small dry pan on high heat with a lid. (Discard the water). Within a few minutes, the clams will steam and open. At this point, gently lift them from the pan and set aside. (If clam does not open, discard the clam). Pour the liquid (clam liqour) from the pan into a measuring cup to allow the grit and sand to settle. Leave undisturbed as you continue with the recipe. Once the clams are cool enough to handle, work above a bowl to scrape the flesh out of the shell, capturing the liquid (liquor) in the bowl. Pour this liquor to the measuring cup with the other liquor from steaming. Rinse the clam flesh well and chop finely. Set aside.
Chop shrimp and squid in bite-size pieces. (You may wish to leave a few shrimp whole to decorate individual servings.) Set aside.
Add oil to a medium heavy-bottom pot. Place on medium-high heat. Add garlic and saute until garlic becomes fragrant. Do not brown.
Add the seafood (except for the whole shrimp, if using) and stir for a few minutes. Add the wine, water, chopped tomatoes, and parsley stems. Season with salt (about 1 tbsp) and black pepper. Bing to a boil and then reduce heat to medium. Slowly add the clam liquid, making sure to leave the grit and sand on the bottom of the measuring cup. Simmer for about 40 minutes. Taste the broth and adjust seasonings. It should be flavourful. (This step can be done earlier in the day or refrigerated.)
Once you are ready to make the risotto, remove and discard the parsley stems. Strain the stock and set the seafood aside. If refrigerated, slowly bring the stock to a simmer.