The assessments will monitor the Devil’s Brook and two tributaries of the River Stour – the River Tarrant and the Pimperne Brook – over the coming months.
Wessex Water is carrying out the work to understand the effect of current abstraction and how this may change following the construction of a new water supply grid.
The grid scheme will connect up water supply pipelines and sources, allowing communities to be supplied with water from more than one source, and it includes a new service reservoir that is currently being constructed at the Sturminster Marshall site.
Wessex Water project manager Ian Colley said: “Following discussions with the Environment Agency and local community groups we will look to see how abstraction currently affects watercourses in the Devil’s Brook and Middle Stour and how this may change once the grid is finished.
“We are committed to protecting the local environment and through the study we hope to find out if we need to be doing more to protect the local river flows.”