The same tea leaves are green when soaked in pure water and yellow when soaked in tap water. What happened?

Tap water passes through a long pipe, which contains a lot of iron. The compound of iron and alkaline substances in tea is reddish brown, and it turns yellow when mixed with the light green tone of tea soup itself. Not only does it look bad, but it also does great harm to the fragrance and taste of tea, so make tea with good water. Pure water is much better than tap water.