Think of John Singer Sargent and you think of oil paint; of the cool, rich palette of his Edwardian society portraits. But the Dulwich Picture Gallery’s latest exhibition, Sargent: The Watercolours, introduces us to a different side of the Anglo-American artist. A looser, freer, less rigid Sargent strides forth, but one, it must be said, that is just as technically proficient.

But tired of the oppressive swagger of portrait commissions at peak celebrity, Sargent turned to watercolour. For Sargent, watercolour offered freedom from the strictures of the studio and light relief from the conventions of portraiture. Composed en plein air, away from the creaking easel and stilled air of a studio, these Impressionistic sketches capture light and flowing water as never seen before in his career.

The exhibition at Dulwich Picture Gallery is curated by Sargent’s great-nephew, Richard Ormond, widely acknowledged to be one of the leading authorities on the artist. Ormond has organised the show thematically into four sections: fragments, cities, landscapes and figures. Sargent's watercolours of the city of Venice, which dominate the second gallery, are among the most insightful in the show.

John Singer Sargent, The Church of Santa Maria della Salute, Venice, c. 1904-9

Entranced by the translucence of Venetian light, the city would provide Sargent with inspiration for more than twenty years. While the subject matter of his Ventian compositions may not be progressive – we see gondolas, canals and palazzos aplenty – the perspective certainly is.

The low vantage point from which Sargent often painted, has come to be known today as the ‘gondola perspective’. By employing this perspective in his Venetian compositions, Sargent invites us to see what he sees. We see the base of a statue rather than the whole, or part of a palazzo rather than the whole. Collapsing the metaphorical fourth-wall with this perspective, Sargent establishes an intimate bond between subject, painter and viewer.

Sketching on the Giudecca, c.1904, is an exquisitely realised example of this unorthodox approach. By including the front of the gondola from which he paints in the composition, Sargent invites us to join the party. The sun beats down on us, the canal water flows around us. Thanks to his thick daubs of white impasto, and light washed tones of yellow, brown, blue and mauve, Sargent’s water glistens and gleams. We are plunged into his world.

John Singer Sargent, A Glacier Stream in the Alps, c. 1909-11

But Sargent didn’t just paint Venetian canals. We see fountains, mountain streams, lakes and cascades in the exhibition as well. San Vigilio, 1913, captures the tranquility of Lake Garda's waters in northern Italy with remarkable proficiency. The bobbing rowing boat and lapping water evokes longed for holidays where long-summer days are spent languishing in hidden creeks and coves. The sense of urgency in his brushstrokes, the surprisingly vibrant palette, the glisten, the sheen and the sensuality of his surfaces transform his landscapes into dreamscapes.

His watercolours may not be challenging nor are they deeply emotional. In fact, the last room, populated with woefully passive figures – predominantly of Sargent’s nieces, female friends and sisters reclining in gardens, parks or by brooks – is deeply unemotional. But they are pretty. Given Sargent has always been about pretty, why should his watercolours be any different?

John Singer Sargent, A Turkish Woman by a Stream, c. 1907

We have seen a lot of Sargent in recent years – The Royal Academy presented an exhibition of his marine works in 2010 while the National Portrait Gallery presented an exhibition of his portraits in 2012 – but this exhibition offers a new angle on the artist. They present his watercolours, previously dismissed as travel souvenirs, as an integral and stylistically revelatory part of the artist’s oeuvre.

This looser, lighter, more fluid Sargent, is quite frankly entrancing.