If Hampstead Heath were in, say, Doncaster, rather than north London, would anyone publish a 176-page glossy, all-colour coffee-table book on the history of its swimming pools and ponds? Hmm. Well, in all likelihood, probably not. But then, it's unlikely that Doncaster's pools would be able to boast publicity blurbs from Melvyn Bragg and Michael Palin and reminiscences of visits by Katharine Hepburn and Margaret Rutherford. "She was enormous," a swimmer tells Caitlin Davies, the author of Taking the Waters. "Like a battleship." And she swam, as many did until the 1950s, stark naked.

There's been public swimming on Hampstead Heath for more than 200 years since the Heath Springs were leased to the Hampstead Water Works company and work began on a series of reservoirs to provide water for London. These became a mixed pond (where both sexes can swim, and which a 19th-century postcard called "the Cockney child's seaside"), a men's pond (where Frank Bruno and John Conteh trained in its gymnastic enclosure in the 1970s) and, prettiest and most secluded of all, the Kenwood Ladies' Bathing Pond.

Swimming here, writes Davies, is "magical, even biblical" and the book, with its archive photos of men performing swallow dives, and women winter swimmers cavorting in the snow (the Times in the 19th century noted these winter bathers were "an inoffensive kind of lunatic"), is the work of a passionate hobbyist.

Davies charts the highs and lows of all the ponds  and when an open-air lido opens in the 1930s, of that too  as well as the threats to their survival and the changes in social mores. There's the ruckus at the men's pond in 1991, when it was cleaned and dredged  four guns were found in the mud  and a rearguard action saw off a proposal to introduce hot showers. There's the OutRage protest led by Peter Tatchell when an attempt was made to ban nude bathing (since the 1960s, the men's pond has been a popular gay cruising ground).

And then the latest machinations, in 2005, when the Corporation of London, which manages the Heath, introduced charges and attempted to shut the mixed pond down. It failed and, for the time being at least, the ponds are safe, a fact not entirely unrelated to its celebrity habitués, high-powered advocates (the leader of the working group was a City lawyer) and friends in the media (Davies quotes not one but two Guardian journalists).

As social history, it's well researched, and colourfully told, but it's also unashamedly niche. Swimming is democratic and the Heath is common land, open to all, but as one of the regular winter swimmers tells Davies it's also "very 'Bloomsbury' somehow and very cultured".

As magical as the Kenwood Ladies' Pond may be (and I for one, can vouch that it is), an incredible patch of green in a city of 8 million souls, there's no disguising that this book suffers from that well-known publishing phenomenon: north Londonitis. It's a thin sliver of history from one of London's least common neighbourhoods, and I suspect the story of public bathing in Doncaster may well never be told.