Water world.

Next to Aaron Betsky's house on a polder 18 feet below sea level is a small grey box with a red light. It contains an emergency switch for the pumps that keep the surrounding grid of picturesque ponds and canals at bay. If the red light comes on, he's probably going to get wet. There is a Dutch saying that 'God made the world, but the Dutch made the Netherlands', clawing back land from the watery grasp of the North Sea and the Rhine. There are 3500 polders (areas of reclaimed land) in the Netherlands, so the Dutch clearly enjoyed playing God.

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Currently director of the Netherlands Architecture Institute (NAI), Betsky, like his Rotterdam Biennale compatriots George Brugmans and Adriaan Geuze (of West 8), are acutely aware of the precarious truce brokered between the Dutch and nature by centuries of ingenious water engineering. The Flood, the theme of Rotterdam's second architecture Biennale, thus had a clear local and global agenda, from the meticulous mapping of polders, to the wider and more corrosive effects of global tourism on coastlines around the world, given hideous momentum by last year's tsunami in the Indian Ocean.

Biennale goings on were split over two main sites, the NAI itself and the decaying Las Palmas warehouse, an atmospheric industrial relic on a nearby quayside. The trio of shows at the NAI focused on a diversity of water-related aspects, such as the historical development of the polder, which so rationalises and defines the Duch landscape, and a comparative study of three geologically similar bays (Tokyo, Venice and Amsterdam) that spawned thriving but very different water cities following initial land reclamation in the sixteenth century. The third exhibition, Flow, curated by artist Saskia van Stein, took a more abstract approach, presenting a series of landscape projects inspired and determined by water's dynamism, rather than fighting and containing it. Yusuke Obushi, for instance, proposed a giant 'Wave Garden', a membrane made up of 1700 elements, floating off the Californian coast that could generate electricity through the undulating motion between individual parts.

Provocative speculations on the Netherlands' future relationship with water continued with New Dutch Water Cities staged on the top floor of the Las Palmas warehouse, accessed by a monumental and precipitous scaffolding staircase shrouded in blue plastic to resemble a giant waterfall. Here, among other projects, was MVRDV's stilt housing, that could be periodically jacked up in case of flooding, and an investigation into the rites and rituals of funerals over water ('21st Century Styx') by students at the Amsterdam Academy of Architecture and Design.

Mare Nostrum, the large international section of the Biennale, also in Las Palmas, surveyed the effects of tourism, now the world's largest industry, on coastline development and communities from the Lebanon to Scotland. Curated by Morag Bain, the Scots presented proposals for five 'coastal machines' (Scotland has an astonishing 6000 miles of coastline) which mixed the practical with the polemic, from GROSS.MAX's notion that the effects of global warming could be countered by using an existing power station to create a giant nuclear iceberg, to Block Architecture's 'Seacrofts', man-made archipelagos of containers on platforms that re-establish the relationship between the Isle of Skye and the Scottish mainland.

Curating Australia's contribution ('32 000 Beaches'), Leon van Schaik also commissioned five architects to consider different aspects of Australia's coastline. Eighty per cent cent of the Australian population lives within 100km of the coast in cities that make an immense demand on the continent's water resources. Donovan Hill's visceral montage 'brisbanemustburn' showed flames of aboriginal land burning apocalyptically lapping the Brisbane beachfront as nature finally takes revenge for historic abuses of ecology. In the plethora of slightly self-regarding Biennale awards, best entry went to 'Al Caribe' from Supersudaca that forensically examined the social and economic consequences of mass tourism on the Caribbean in general and the north coast of the impoverished Dominican Republic in particular.

If the ponderous juggernaut of Venice is anything to go by, Biennales have a sacred duty to be irritatingly diffuse, both physically and intellectually, but Rotterdam was decidedly more focused (to the point of only lasting a month) and had a sense of coherence, even though the Dutch obsession with polders is perhaps not shared outside the Low Countries. In the astute choice of a theme that had both local and global resonance it imaginatively connected history with speculation and offered new insights into humankind's immemorial and often troubled relationship with water and the wider planet.

www.biennalerotterdam.nl