Clouds of condensation can sometimes be seen rising from manholes in Manhattan , although this is usually caused by external water being boiled by contact with the steam pipes , rather than leaks in the steam system itself .
Clouds of condensation can sometimes be seen rising from manholes in Manhattan through red - and - white '' chimneys '' . 
 This can be caused by external water being boiled by contact with the steam pipes or by leaks in the steam system itself .