GST 18 applicable RO water

Sir,

i have installed RO plant outside at my home. I have sold ro water 20 Paisa per litre.means monthly card RS 120 and 600 liter water to per customer. Coustmer bring Bucket,, drum, bottle from home come to my house open the tap fill the water and go back to home. sometime farmer come to my point and filed 1000 liter drum water. i don't sale any packing bottle water sealed water etc. my neighbour told me you are sold ro water so you are Pay GST 18%. it's ro water per it's loose water so any gst applicable on me. please suggest.