Few well-controlled studies have investigated the impact of poor quality water on pig performance; most suggest the pig is capable of handling relatively high concentrations of sulphates and other mineral contaminants without apparent effect. However, claims from field workers suggest that under farm conditions, water quality is an important issue that has not yet been adequately addressed. Two experiments were conducted to determine how pigs react to poor quality water under commercial farm conditions. They were carried out on a commercial farm, where the well water was high in sulphates, total dissolved solids and iron; an on-site reverse osmosis unit provide high quality water for comparison. Although diarrhea was observed, water quality had no impact on weanling pig performance or nutrient digestibility. Based on these results, along with previous research, it can be concluded that pigs weaned at three weeks of age have the ability to handle relatively high quantities of sulphate in their drinking water and maintain overall growth performance. It can further be concluded that the presence of diarrhea alone, associated with high sulphate water, cannot necessarily by linked to poor animal performance.