Water Soluble
noun
With water it will melt. It is naturally like this. It is water soluble.
すいようせい
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
水溶性のビタミンCはすぐに体内から排出されるので、私達の体に蓄えることはできないと読みましたよ。
I read that water-soluble vitamin C generally leaves the body quickly, so our bodies can’t store it.