i dont know what it is, but my guess would be an addetive that makes the water sheet on every window, or an anti freeze if so its a chemical. while using wfp it is impossible to not breath in fine water vapour. i would stop using it. there is also evidence to show that water that has been through di resin contains some extreamly nasty chemicals, i would argue that di is not needed at all if your RO can produce at 5ppm or less.
remember wfp is new technology DI resin was not developed for wfp, but industrial use. i wonder if in 50 years from now there will be ex wfp window cleaners with health problems. we have not used DI resin for months with no complaints from customers.