To provide a plug for water conduction capable of preventing a filter from damaging and also preventing fine particles of viscous soil from sticking on the filter.

A plug for water conduction includes a plug body 6a, and a filter 7 and a filter protective member 8 provided in a through hole 6d thereof. The filter protective member 8 has a plurality of protective member water conduction holes 8a, which are filled with a water-soluble substance SB, so when a steel material 2 is cast in the ground, the water-soluble substance SB is prevented from being ground away. Therefore, the filter 7 is protected by the water-soluble substance SB and fine particles of viscous clay is therefore prevented from sticking on the filter 7. Further, the filter protective member 8 is provided, so when the steel material 2 is cast in the ground, the filter is prevented from damaging with sediment.