In all these cases the simplest method is the best, provided the supply of water is not needed in the winter; but such simple methods as just described fail when frost locks up the surface flow of the stream. Then the pipe throughout its entire length must be in a trench below the frost line at the entrance to the spring as elsewhere. To permit this, the spring must also be deep, or else so inclosed that the pipe leading into the spring can be covered by earth banked up against it. Not long ago the writer saw a pipe taking water from a small lake recently improved by a stone wall. Instead of conveying the water-pipe down under the wall the unwise stone mason had built the wall around the pipe and the pipe line was frozen up through the entire winter following. Such simple methods also fail when the supply of water is not adequate, since, in order to secure a large quantity from a stream whose flow is periodic and irregular, some storage must be provided, and storage usually requires more or less elaborate construction work at the reservoir. Another reason for more elaborate construction at a spring is to prevent surface contamination, and it is always desirable to roof over a spring in order to protect it from surface flows. The writer has seen, as an example of objectionable construction, a spring in the bottom of a ravine or gully down which, in time of rain, torrents of water passed, although in a dry season the spring was the only sign of water in the vicinity. It could not but happen that this torrent of water, which carried all kinds of pollution from the road above, practically washed through the spring, destroying its good quality. In such a case, another channel for the gulley water ought to have been made, or else the spring dug out and roofed over, so that the torrential water could pass above it. In other cases, the spring is found at the lowest point in a general depression, so that, while no stream passes through the spring, the spring is a catch-all for the surface drainage in the vicinity. In such cases the water should be protected by a bank of earth around the spring, behind which the drainage should be led off through a special pipe line if necessary. _Spring reservoirs._