Pure water has a low pH

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A separate closed-cycle cooling tower was built for the air compression station, and it is operated using pure water supplied from the power plant. However, since its operation began, the pH of the soft water in the pipes and the spray water has remained on the acidic side. The pH of the pure water from the power plant was measured at 6.25, while the pH of the spray water and the soft water in the pipes was 5.7 and 5.3 respectively. The closed-cycle cooling tower built specifically for the hydrogen compression station also uses pure water; in that case, the pH of the spray water is 5.7, and the pH of the soft water in the pipes is within the acceptable range. The required pH range is 6.5–9.0. The pH of the pure water from the power plant is already low, and it becomes even lower once it reaches our system. The pH of the spray water might be affected by carbon dioxide in the air, but surely not to such an extent? Is there anyone experienced who can give some advice?