The aqueous substance, for example sea water, is boiled, the steam produced is fed under pressure into a turbo-alternator turbine producing electricity, the residual steam is reduced into soft water and the residue of evaporation, for example sea salt, is recovered as a by-product.The steam is fed directly or on leaving the turbine onto iron heated to about 800.degree. C., which supplies hydrogen and as a by-product ferric oxide. The initial source of energy is, besides solar energy, any known source of energy, such as coal situated at great depths. The starting aqueous substance is, apart from sea water, waste sludges, a rock salt solution or a mixture of sludges and salt solution. In the case of sludges, the by-product is a dry and sterilized fertilizer transformable into fuel bricks. The salt residue is transformable by electrolysis into hydrogen and sodium chlorate, which is a fuel. The sludge-salt residue supplies a combustible mixture. Dried sludges-sodium chlorate, is mixable with household waste for promoting the combustibility thereof. The sodium chlorate can be transformed into potassium chlorate and the steam under pressure may be condensed in distant reservoirs and its heat recovered. The energies produced in the turbo alternator or fuel-by products are usable in the process.