In a clean glass or ceramic jar, layer the anchovies with the sea salt. Add filtered water, ensuring the fish are fully submerged. Cover loosely with a cloth or lid. Let the mixture ferment at room temperature (around 20-25°C / 68-77°F) for 6-12 months, stirring occasionally. After fermentation, strain the liquid through cheesecloth or fine sieve to separate the fish solids from the liquid. Store the strained fish sauce in sterile bottles or jars. Optionally, add a touch of sugar during fermentation to enhance flavor. The longer it ferments, the richer and more complex the flavor becomes.