A year or so ago grey water started spouting, intermittently and unpredictably, from plugholes in the kitchens of a number of flats in our building. Plumbers were called and over a number of weeks denied the existence of the problem, confessed themselves unable to solve it and explained that 60 years of ad hoc plumbing in each flat had rendered the whole system incomprehensible. Then, when they finally obtained the plumbing equivalent of 'root', they discovered that someone had poured the entire contents of a substantial aquarium down a toilet. This had, unsurprisingly, messed with the delicate and contingent balance of pressures and flows within our pipes. That someone does not understand our invisible infrastructure. Our plumbing is incomprehensible. These are not new problems.