Until the recent fears of terrorists polluting our waters, reservoirs hardly made the headlines. Except in Cambridge. A few years ago, the artists Mags Harries and Lajos Heder proposed an outdoor artwork for the new Cambridge Water Works' building at the Fresh Pond Reservoir.

Miraculously, Harries and Heder overcame such odds - including a strangely incongruous fountain, designed by the architects, that appears to be thrust into their site. Cambridge should be proud of the result. Making visible what is hidden, the artists have used differing widths of copper, inset within the colored stone floor, to represent the city's water pipes, fountains, pools, ponds and river. Many of the pipes follow the city's streets, some of which are marked, making it easy to locate oneself within this miniaturized Cambridge.