http://www.thehorse.com/articles/31418/researchers-identify-link-between-insulin-resistance-iron-overload
There is a link between excessive iron and insulin resistance.
As for iron in water, see: http://www.thehorse.com/articles/12753/water-contamination
"The most reliable indicator of water quality in your barn is the total amount of dissolved solids (TDS), a number that can easily be determined with a water test run by your county or state health laboratory, your local agricultural extension agent, or the Environmental Protection Agency. TDS is the sum of the concentrations of all organic and inorganic substances dissolved in the water, including mineral salts, algae, bacteria, nitrates, and solid particles of debris. Levels below 1,000 parts per million (ppm) TDS is considered satisfactory for livestock. Levels between 1,000-5,000 ppm are considered satisfactory, although they might cause a mild, temporary diarrhea or refusal of drinking water. Levels over 5,000 ppm should not be used for lactating animals or for animals in late gestation. At levels over 3,000 ppm, your water might have an offensive smell, taste, or color.
Well water often contains significant concentrations of dissolved minerals, which can influence the taste, smell, and palatability of your water. (The classic example is “sulfur water,” which has that unmistakable rotten egg stench.) Your local lab can test your water for levels of calcium, magnesium, manganese, iron, copper, zinc, sodium, chloride, and lead, as well as sulfates and nitrates (nitrate contamination is particularly common on horse farms; its likely source is your manure pile). Concentrations of these minerals, if sufficiently high, can also have an impact on your horse’s dietary balance, since levels of one mineral in his gut can often influence his ability to absorb another.
Some minerals, such as iron, calcium, and magnesium, are chiefly concerns because they can clog your plumbing with scale and deposits, and change the water’s color and taste. Other minerals, such as lead, are more worrisome because they can build up to toxic levels."
Then there is this article:http://www.howtodothings.com/how-to-remove-iron-from-well-water
"There are many ways to remove iron from water. Solutions range from a simple cartridge filter to more expensive ozonation systems, depending on solubility, iron content and acidity of the water.
Insoluble iron may be taken out using filter and would require change in filter only after the filter has been saturated or clogged. If the iron is in a soluble form, treat the water first through chlorination, aeration, catalytic filtration and Ozonation. Once iron is insoluble, filter it out. The only drawback is that once these procedures have been started, they should be done regularly for maintenance. Also, it costs about $800 to thousands to have these performed.
The type of procedure also depends on the amount of iron and the pH. If the iron content of the water tested is found to be more than 10 parts per million (ppm), purchase a filtration system that can chlorinate and act as a mechanical filter in order to remove rust particles. If pH is less than or equal to 6.8 and water has 0.3 to 10ppm of iron, using water softeners alone may be able to take out not just the excess iron, but other metals such as calcium and manganese. In addition, it can also increase sodium content through ion exchange mechanisms. If pH is greater than 6.8 and iron content is 0.3 to 10ppm, simply use filters as these oxidize and absorb iron."
