Yes, the 16 ounces of water is by weight. You can tell by the fact the weight of water is also given in grams. One pound is about 452 grams in the metric system (the more accurate value is 16 x 28.35 = 453.6). The flour in your recipe is also by weight since the gram equivalent is also given. In most cases, flour is recited by weight, not volume. Where things get confusing is where a liquid ingredient is specified in only ounces. For example, if a recipe lists, say, 12 ounces of oil, and nothing more, there is no way to know whether the measurement is 12 ounces by weight or 12 ounces by volume.