I can't speak about the potential of metals being drawn into the water with DI, RO, or distilled only water. But I can verify from personal experience, that ultra purified/polished water will attack metal components, to the point of destruction.
Many years ago I was managing an automotive seat belt test lab. It was a new facility, and the lab manager from a sister facility had a company design a water purification system. The purified water was used for salt fog testing, and also for the humidity generator on the environmental chamber. The water first went through a pair of sediment filters, then a charcoal filter. Next was a water softener, then a pair of DI tanks. Last was an RO system. From there, the water was used to make brine solution for the salt fog chamber, and also supplied water for the humidity generator.
Before long, we had problems with the electric heater elements failing in the humidity generator. When we replaced the heater elements, we found that the copper tube had been eaten through on the old heater element, resulting in the failure. This happened a few times before we called in an expert to help us.
The expert determined that our water was over polished, to the point that it was drawing metal from the components of the water generator system. The copper tubing on the heater elements was the softest metal, so it always got attacked first. We changed the piping, so the water for the humidity generator was sourced after the DI tanks, but before the RO system. This did the trick. We never had to replace another heater element.
Of course, this was not a closed system, like a cooling system on an engine. Instead, water was constantly consumed and replenished, to generate the humidity needed in the environmental chamber. But water can be too pure.
