Composite words In environmental science the most commonly combined word is water when used with fresh, salt, lake, sea, ground, melt, tide, etc. As adjective plus noun, they are written as two words (Fresh water is good to drink); when they form an adjective, they are written as one word (Freshwater clams are good to eat). The exception is brackish-water. Other composite words include badlands, bedrock, borehole, coastline, crosscut, crossbedding, downstream, downlake, downfiord, drillhole, footnote, hardpan, hillside, hilltop, hydroelectric, iceberg, lakebed, landform, landlocked, macrofauna, motorboat, mountainside, mudcrack, ongoing, overflow, overland, override, overrun, percentage, pipeline, pothole, postglacial, quicksand, radioactive, radiocarbon, rainfall, seacoast, shoreline, sinkhole, snowfall, snowfield, snowline, strandline, tableland, treeline, ultraviolet, underflow, uplake, upfiord, upstream, waterfall, waterline, and watershed. But compare base line, bench mark, clay belt, field work, flood plain, flow line, ground level, ice cap, ice dam, ice field, ice sheet, ice front, per cent, rain water, water level, water gap. See Hyphen.