Any dirt or grit or sand will sink to the bottom. Skim the spinach leaves off the water with a colander and let the dirty water out of the sink. Repeat the process. To cook fresh spinach, dump the drained spinach into a pot. Leaving only the water clinging to the leaves from its wash, cover the pot and cook for 3-5 minutes.
Spinach is a delicate leaf that cooks rapidly.
If it is overcooked, it loses its tenderness and sweet flavor. It gains only in toughness and slime. Drain the spinach and that's it. Spinach does not like to be boiled. All of its goodness is lost to the cooking water.