Solar salt is in most cases produced from seawater brine. Occasionally brines also originate from salt lakes, natural underground brine sources, or dissolved rock salt. In a salt field, brines are led through a series of ponds, where the water evaporates. When the solution reaches the point of saturation, salt crystallizes and can be harvested. Salt is dried and re-washed to remove occluded liquor and surface impurities to provide high specification material. This salt is usually purer than rock salt. Given that the energy for the evaporation of water comes from the sun, salt from solar sources has the lowest carbon footprint and can be relatively cheap. Of course, solar salt can be produced only where a favourable climate, and geography permit. Depending on the climate, harvesting can be done one or two times per year.