def __calculate_waterfootprint(wf_ing, quantity):
    """
    Calculate the right water footprint of a ingredient from its
    (l/kg) water footprint and the quantity provided (in gr).

    :param wf_ing: the water footprint of the ingredient.
    :param quantity: the quantity of the ingredient.
    :return: the water footprint calcuated on the quantity.
    """
    return round((wf_ing * quantity) / 1000, 2)