Since it's on city water, I'd suggest checking the pressure and tap water TDS, even though pressure shouldn't be such an issue on most municipal water systems. Some of it could just be picking the wrong time of day to make water -- during certain times of the day, the pressure at our house is as high as 100 psi, while there are times during that same day that I've seen it drop to 60 or 70 psi without us running any water in our house. What the neighbors are doing can have a big effect on water pressure. If the TDS is really high, it could be slowing production rate a little bit as well.