Scotland's water watchdog has accused regulators of not being tough enough on water firms who make it hard for small businesses to change suppliers.
There are five companies licensed to provide water in Scotland.
But one, Scottish Water's subsidiary Business Stream, has a 90% share of the non-domestic market.
Waterwatch Scotland (WWS) said the virtual monopoly existed because small businesses found the process of changing supplier too complex.
It also claimed complaints about Business Stream were going up - particularly over billing - because it did not have enough competition.
Waterwatch Scotland said regulator the Water Industry Commission should do more to force firms to make it easier to switch.
It suggested that would bring in more suppliers and result in better deals for customers.
In its first report on retail competition, WWS also claimed there was a potential clash of priorities for the Water Industry Commission as it acted as both market developer and market regulator in Scotland.
WWS convener Heather Brash said that, while Scottish Water's services to domestic customers were improving, services for many non-domestic customers were not.
She said: "What we have at the moment is one dominant player generating a marked increase in customers raising issues with the industry watchdog, and little evidence that the necessary steps are being taken to address the monopoly by making the option of switching a well publicised and straight-forward option for all businesses in Scotland."