The mass won't change, so 1 kg of liquid water will form 1 kg of steam. Taking the density of water to be 1 g/cm³, you need 1 L of water to produce 1 kg of steam (in actual fact, you need a bit more, since water is not quite that dense). To make 1 ton of steam, assuming you use a metric ton, you need 1,000 L of water.