Before the business market was opened to competition there was no distinction between retail and wholesale services. Businesses were supplied exclusively by their regional water or water and sewerage company, just as households still are. In the new market, wholesale and retail services are provided by different companies who have different responsibilities.
Wholesalers provide water to the customer through the same pipes and networks as before with some also managing the removal and treatment of wastewater, but they no longer perform any customer-facing activities. Instead, they charge a wholesale rate to a retailer who passes the charges through to the customer, adding a small retail fee for providing billing, meter reading and customer services.
If you experience a water or wastewater emergency such as no water, a burst main, taste/smell issues with the water at your property or you are aware of a blocked public sewer you will need to call your local wholesaler, not your retailer.