=Amsterdam.=—The water is derived from open canals in the dunes. These canals have an aggregate length of about 15 miles, and drain about 6200 acres. The water, as it enters the canals from the fine dune-sand, contains iron, but this is oxidized and deposited in the canals. The water after collection is filtered. It has been suggested that by using covered drains instead of open canals for collecting the water, the filtration would be unnecessary; but, on the other hand, the cost of building and maintaining covered drains in the very fine sand would be much greater than that of the canals, and it is believed, also, that the water so collected would contain iron, the removal of which might prove as expensive as the present filtration. In 1887 filters were built to take water from the river Vecht, but the city has refused to allow the English company which owns the water-works to sell this water for domestic purposes, and it is only used for public and manufacturing purposes, only a fraction of the available supply being required. Leyden, the Hague, and some other Dutch cities have supplies like the dune supply of Amsterdam, and they are invariably filtered. =Antwerp= is also supplied by an English company. The raw water is drawn from a small tidal river, which at times is polluted by the sewage of Brussels. It is treated by metallic iron in Anderson revolver purifiers, and is afterward filtered at a rather low average rate. The hygienic results are closely watched by the city authorities, and are said to be satisfactory. =Rotterdam.=—The raw water is drawn from the Maas, as the Dutch call the main stream of the Rhine after it crosses their border. The population upon the river and its tributaries in Switzerland, Germany, Holland, France, and Belgium is very great; but the flow is also great, and the low water flow is exceptionally large in proportion to the average flow, on account of the melting snow in summer in Switzerland, where it has its origin. The original filters had wooden under-drains, and there was constant trouble with crenothrix until the filters were reconstructed without wood, since which time there has been no farther trouble. The present filters are large and well managed. There is ample preliminary sedimentation.