The direct health implications of iron are very limited, there are however indirect problems some of which are: colour, which comes from iron in a particulate form which is too small to filter so you get “coloured water”, iron bacteria, this is when bacteria and iron form a slime which can lead to poor pipe flow, this can occur when the iron concentration exceeds 0.3 mg/L, the Canadian Drinking Water Guideline (CGLS).
Most countries, including Canada, have set an aesthetic rather than a health guideline for manganese. The reason for this is that levels above the guideline can stain porcelain and laundry, drinks such as coffee and tea can become cloudy and taste funny. High manganese levels can also cause diarrhea.
There are many negative health effects related to Nitrate, some of which include blood deficiencies, thyroid problems, decreased vitamin A, and cancer. It is, however, rare that nitrate levels are above the Canadian Water Quality Guideline for drinking water. Contaminated private wells are likely the most common place where high levels of nitrate are found.