(1) The common mineral elements in groundwater are iron, sulfur, chlorine and magnesium. These minerals can form complexes with calcium, magnesium and sodium. And form total soluble substances in water. It is reported that when the total soluble matter in water exceeds 5000 mg/L, it will cause diarrhea in pigs, affect production performance and reduce the exercise ability of pigs.

(2) Nitrates harmful to pigs may exist in the water. Nitrate exists in the surface and groundwater, and can be converted into nitrite, which is toxic. Nitrate is toxic only when it is converted into nitrite. It is safe that the concentration of nitrite in water is lower than 100 mg/kg, but when the concentration of nitrite in water is higher than 100 mg/kg, hemoglobin can be converted into methemoglobin. Methemoglobin in blood can't deliver enough oxygen to tissues. If the content of methemoglobin in blood is too high, it may lead to the death of pigs.