The water garden, designed by Harold Peto for the 1st Lord Faringdon at the beginning of the twentieth century (photograph published in the Architectural Review in April 1913)
 
Campbell’s improvements to the park and gardens, along with his creation of a number of boundary plantations and his opening up of various vistas, laid the foundation for the most exciting phase in the garden’s development. When Alexander Henderson acquired Buscot Park in 1889, he employed the Ernest George Partnership to enlarge the mansion and build various cottages, farm and public buildings in Buscot village. It was through Ernest George that the renowned landscape architect, Harold Peto, was then invited to Buscot to work on improving the links between the house and the lake.

Peto was a former partner of Ernest George, leaving in the early 1890s to establish what subsequently developed into a substantial garden design practice. Peto worked much in the Mediterranean and was a leading exponent of the revived principles of Renaissance garden design, as well as an avid collector of antique, Gothic and Renaissance architectural fragments. At Buscot Peto laid out the renowned water garden between the north-front terraces and the lake. He also added a new forecourt to the south front of the mansion, adding balustraded walls and stone gate-piers. Next to the forecourt he planted a semi-circular sweep of yew hedging to contain the figure of Diana returning from the Chase, which he had purchased in Rome.