A Group U doesn't require an automatic sprinkler system so long as its height and area isn't exceeded. The sprinkler issue may be driven by the stored hazardous materials or it could be a local amendment by the Fire Department or Fire Authority. Some water disinfecting chemicals are Oxidizers and most all are Corrosives. The Maximum Allowable Quantity (MAQ) per Control Area values in IFC Table 5003.1.1(1) for physical hazard hazmats sets the MAQ for the respective classes of oxidizers; Table 5003.1.1(2) sets the MAQ for Corrosive and/or Toxic materials, depending on its physical state.
More than likely the jurisdiction will require an IFC Hazardous Materials permit and IFC Section 5001.5. Being in California, this can be the Certified Unified Program Authority, which could be the Fire Department or Health Department, depending on the County. As part of the permit, a hazardous materials inventory statements (HMIS) will need to be generated. The HMIS can be compared to the MAQs to determine if your client is exceeding the quantity limits. Note that an automatic sprinkler system is not the only option allowed by the IFC to increase the MAQ, meaning an automatic sprinkler system isn't required in all cases.
If the inventory is short (<4 chemicals) I can offer a better opinion.