Add water, carrots, onion, celery and fish bones to a large stock pot. Slowly bring to the boil skimming any scum from the surface of the water regularly. Add the herbs and the peppercorns, reduce the heat and simmer gently for 20 minutes.
Strain through a fine sieve lined with damp muslin. Discard all the solids and allow to cool. Refrigerate and remove any set fat from the surface of the liquid.