Probably about 400 to 500 ml, that is, about half a liter or less.
An electric iron is merely a resistance element built into a casting (normally aluminum) - the soleplate. A steam iron works by facilitating the controlled release of water onto the heated soleplate. As you know, this happens by pressing a button on top of the iron handpiece. When the button is pressed it opens a 'tapered needle valve' which then releases water from a water reservoir. This water slowly dribbles onto the soleplate. The soleplate will have been treated with a suitable surface treatment (that affects the surface tension of the water) causing it to instantly vaporize, which is the steam that is then vented through the small holes you can see in the soleplate.
Distilled water - because it contains no other contaminants that could be detrimental to the iron.
Fe is the chemical symbol for iron. When iron reacts with steam it corrodes, or rusts.
Most ordinary tap water contains dissolved minerals. When the water evaporates, or is boiled away to produce steam as in a steam iron, these dissolved minerals remain. Eventually, in a iron, they will accumulate to clog up the channels and water reservoir in the iron rendering it useless. Hence the necessity of an anti-scaling device or means of removing them.
The iron may be dribbling water because the water reservoir is overfilled or because the steam settings are too high. Excess water in the iron can leak out during ironing, especially if the iron is moved too quickly or tilted at an angle. Try draining some water from the reservoir and adjusting the steam settings to see if it helps reduce the dribbling.
Iron is to shirt as steam is to pants.
Iron is corroded in steam.
Iron and Zinc
So we can see how much the water is up to so if we know if it is high or low approximately how much it is compare to the steam iron.
Iron filings do not dissolve in water. They are small pieces of iron that are insoluble in water and will float or sink in water rather than dissolve.
CLR is a common choice for cleaning mineral deposits in household appliances, but it is not recommended for use in steam irons. The chemicals in CLR can be harsh and may damage the internal components of the iron. It is best to use a mixture of water and vinegar or a specifically formulated iron cleaner to clean the reservoir of a steam iron.
Steam it lightly. If your iron doesn't have a steam setting, use a spray bottle to spray water on the material before ironing. Iron on the side that faces in.