To provide hydrophobic material for a covered conduit and a production method thereof as well as a covered conduit made of hydrophobic material for the covered conduit replaceable as new and cheap hydrophobic material and capable of enhancing drainage, water retention, and air permeability of soil in a farm field.SOLUTION: Hydrophobic material 1 for a covered conduit in accordance with the present invention is made by removing coal content from coal sludge, which is waste produced in a coal mine, having a grain diameter equal to 5 mm or more to equal to 40 mm or less. Preferably, the hydrophobic material 1 for the covered conduit in accordance with the present invention also has a content of silicic acid in an available form equal to 13 mg/100 g or more, a hydrogen ion index (pH) equal to 7 or more and 10 or less, and charged electric accumulation equal to 0.7 nC/g or less.SELECTED DRAWING: Figure 1【課題】新規で安価な疎水材として代替することができ、圃場における土壌の排水性、保水性および通気性等を高めることができる、暗渠用疎水材およびその製造方法ならびに暗渠用疎水材を用いた暗渠を提供する。【解決手段】本発明に係る暗渠用疎水材１は、炭鉱で生じた廃石である石炭ズリから石炭分を除去してなり、５ｍｍ以上４０ｍｍ以下の粒径を有する。また、本発明に係る暗渠用疎水材１は、可給態ケイ酸の含有量が１３ｍｇ／１００ｇ以上であり、水素イオン指数（ｐＨ）が７以上１０以下であり、帯電電荷量が０．７ｎＣ／ｇ以下であることが好ましい。【選択図】 図１
