the ppm is a measure of the solution is used to describe the quality of performance or concentration of a substance in a larger mixture. This could be used to describe contents in water alone or with nutrients. When you mesure the ppm of tap water, yo get the mineral content of the water (calcium, magnesium, etc) when you mesure the nutrient solution you get mineral content of the water + mineral and organic content of the nutrients (n,p,k, etc). Happy growing mate 👨🌾🏻🤝