How effective is rice water as fertiliser?

Testing the effect of fresh and fermented washed rice water (WRW) on the growth of sawi, grown in various soil types. WRW is also compared with chemical fertilizers and control (only tap water). Photos: Christopher Teh

We all wash rice before it’s cooked, and the leftover water, called washed rice water (WRW), is typically just poured down the drain.

But many have claimed that WRW should be reused as plant fertiliser for the nutrients it contains. It is claimed that watering with WRW increases plant growth, encourages flowering and fruiting, and produces healthier soils. But where’s the science?