This is a fun and simple way to begin enjoying the virtues of low-temperature cooking without investing in sous vide equipment. A pot of water preserves a constant temperature for up to 1 hour, far more time than is necessary to cook fishand even enough time to cook some steaks (a picnic cooler keeps the water temperature stable for up to 5 hours!). The more food you put in the water bath, or the colder the food is, the more the water temperature will drop. To help hold the heat, bring the food to room temperature before cooking it, and use your largest pot and an abundant amount of water.
adapted from Modernist Cuisine at Home