Nutrient culture solution was made using four kinds of water. Chemicals solved in solution are all the same, but only water used has different sources; viz, distilled, city, well and pond water. "Kenaf" plants cultured in these four kinds nutrient solution. Plants grown in distilled and city water solution showed the deficiency symptoms of boron clearly, but in well and pond water, no deficiency symptoms appeared. Chemical analysis of these waters by Berger and Troug' s method showed that distilled water contained no boron, city-water 0.007 p.p. m., well-water 0.25 p.p.m. and pond-water 0.65 p. p. m. boron. From these facts, we can expect to estimate the water soluble boron by water culture method using "Kenai" plants as an indicater plant, if skilfully planned.