The announcement that a fountain is to be built in memory of Diana, Princess of Wales, has been hailed by Lord Archer as a "wonderful" idea. But in reality there could be no more conclusive proof that the people's princess has already been consigned to the dustbin of history. For in modern culture, there is nothing more forgettable and pointless than a fountain. To be compelled to gaze at a modern fountain is pure water torture: more pleasure can be derived from watching garden sprinklers, car washes and public urinals. Fountains have become the ultimate damp squib.
It wasn't always thus. Before the modern age, the public fountain was a place where every kind of dream came true. On a practical level, in a period when water was often scarce, and drinking water ever scarcer, fountains were places of daily pilgrimage. From the renaissance onwards, a spectacular fountain was a mark of civic pride - and to this end, the water was free to all comers. In Italy, when an aqueduct had been built (or an ancient Roman aqueduct renovated), the best artists of the day would compete for the honour of designing a fountain bang in the heart of the city.
No wonder that renaissance and baroque fountains exude a sense of inexhaustible energy. Water spurts from mouths, breasts, penises and sometimes even wounds; and it cascades over the ample lips of curvaceous bowls. The creators of these multi-figured monuments believed that water made the world go round. One of the greatest fountains of all is the Trevi fountain (1732-62) in Rome. It was designed by the architect Nicola Salvi, and its opening marked the completion of an aqueduct. It is an allegory of water, with the naked god Oceanus a swaggering master of ceremonies at its centre. According to Salvi's written programme, Oceanus was the "father of all things". In this role, he was not so much "the symbol of the powerful operative forces of water gathered together in the sea" as "the actual working manifestation of these powers, which appear as moisture". As moisture, water "permeates all material things".
The writing had long since been on the wall for fountains when Alfred Gilbert designed the Shaftesbury memorial (1886-93) in Piccadilly Circus - better known as Eros. The sculptor tried to revive the exuberant style of renaissance fountains but he hadn't counted on the machinations of modern bureaucracies. Gilbert envisaged a wide variety of water jets cascading into a large basin, but the need for a parapet (to conform to a city ordinance stipulating the enclosure of all public monuments) and drinking cups and an outcry against a big water bill wrecked all this. A second flight of steps replaced what should have been a lower basin, and the whole fountain was lowered by six feet. Within a week, the drinking cups had been stolen and broken. Some complained about the pathetic trickle of water from the jets, while others complained that the spray made the streets dangerously slippery. The jets were almost immediately switched off. The water from this fountain wasn't allowed to permeate anything.
A stultifying sobriety and pseudo-rationalism has vitiated too many 20th-century fountains. Whereas in renaissance fountains water had an inebriating function - it was, in effect, water transformed into wine - in our century water aspired to the condition of industrial lubricant or chem- ical. Naum Gabo's Revolving Torsion (1976), outside St Thomas's Hospital in London, is a stainless steel crop sprayer-cum-car wash. The Bernini among techno-bores is undoubtedly William Pye. Every reader has probably shuffled past Pye's Slipstream (1988) in Gatwick airport. It is a slick nothing: a stainless steel cone covered in a wafer-thin meniscus of falling water. It could be a public urinal in mid-flush or one of Madonna's conical bras. What a turn-off.
The Diana fountain is as good an exercise as any for a revival of the spirit of renaissance fountains. It should be an unashamed celebration of moisture. We could have something along the lines of a naked goddess standing determinedly astride a landmine, with water spurting from every available orifice. The goddess (an allegory of virtue) could stand in a conch shell, supported by various adoring and permanently soaked paramours. Trampled beneath her feet and semi-submerged in a large bowl of water would be innumerable writhing, grub-like creatures - allegories of the tabloid press. Jeff Koons, Claes Oldenburg, Barry Flanagan and the Chapman brothers are contemporary sculptors who might rise to the occasion.
Doubtless a solution along these lines will be deemed unacceptable to the Royal Parks Agency, which has jurisdiction over any monument erected in the parks. In this age of privatised water companies and third ways, we are more likely to get something that is an exercise in sensory deprivation - a parched, puritanical trickle that can only be an allegory of Lethe, the classical river of forgetfulness.
James Hall's "The World as Sculpture: the changing status of sculpture from the renaissance to the present day" is published by Chatto & Windus at £25