Our London house overlooks a sewer, or what had become one. Fortunately, the notorious watercourse was covered over when Cubitt developed the area, but it explains the curve of the street, in an otherwise rectilinear grid. The sewer still discharged its unsavoury burden into the Thames, however, hence the Great Stink of 1858 when the reek offended Parliamentary noses to the point that they commissioned Bazalgette to construct the sewers.

The problem had not existed in the Georgian period-then, nightsoil-men came to empty the cesspit and sold the contents to market gardeners. As London grew, this exchange became impractical. Refuse was tipped into streams. In the grander areas, it was flushed. The water closet had a lot to answer for. It still does, particularly at a time of drought.

And not just in this country. Emerging nations, anxious to adopt western patterns of life, are flushing their futures away. Hygiene is not the only call on precious water-supermarket vegetables, grown in hot countries, are another-but must be the least necessary. It is perfectly feasible to compost human waste: Alderman Mechi, the Victorian High Farmer, campaigned on this very point, believing Londoners were neglecting a valuable resource. Will this feature as an issue in the mayoral election? Of course not, but perhaps it should.

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