①名词为purity

n. 洁净，纯净；纯洁，清白；（声音、文章、音乐等的）清晰

②动词为purify

v. 使（某物）洁净，净化；变纯净；洗涤（思想），净化（心灵）；提纯，精炼

It can also help to purify the water quality, reduce pollution and improve environment.

荷花还可净化水质、减少污染、改善环境。