Designed by Harold Peto, who was, in his day, the leading exponent of formal Italianate garden design, the Water Garden was laid out in 1904 for the 1st Lord Faringdon, and extended in a second phase of building in 1911 to 1913. The garden creates a link between the house and the Big Lake that is such an important feature of the original eighteenth-century parkland landscape. Consisting essentially of a chain of stairways, paths, basins and a central canal, the Water Garden is flanked by box and cypress hedges, sheltering statues and terracotta jars.

The stone-edged canal follows the bold linear axis of the earlier Victorian arboretum, carried for the greater part of its length through woodland. Variety is given to the design by a series of secretive enclosed lawns, surrounding rectangular and quatrefoil pools, and by effectively placed Italian marble seats and statuary. The canal stream is made to perform every possible manoeuvre before it reaches the lake, running over narrow rills and miniature cascades and beneath a hump-backed balustraded bridge. At one point the water is thrown into the air by the charmingly playful Dolphin and Putti bronze fountain. Water-lilies decorate the surface, and the hedges are flanked by stone figures on columns, and herms portraying Roman gods. Where it meets the lake, the vista continues eastwards to the domed and columned garden temple, also designed by Peto, which sits on the opposite shore.