Mother's secret magic potion

All these while you have been suspecting your mum for practising black magic.

One day late at night, you saw your mother pouring something into a pail in a bathroom.
She added water into the pail until the water brimmed over, and few pieces of clothe appeared on the surface out of a sudden. You saw her laughing to herself while sitting on a stool.

"It seems she really practises black magic!" you told yourself.

You went in the bathroom on the next day and hoped to find out what potion she has used to produce clothes out of water.

Beside a set of brushes, you found a box of powder, which was labelled as 'washing powder'. So you followed the procedure: You poured some powder into the pail and added water into it. You were frightened at first, seeing powder transforming into foams as it dissolved in the water.

You retreated and leaned against the wall behind you, as you watched the foams grow more and more, more and more. Both the bubbles and water overflowed and wet the floor. You turned off the water tap to prevent the floor from getting wet. The bubbles receded and peace was restored in the bathroom.

You felt extraordinarily weird. You mustered up  courage to test the water with your index finger, even though you stood far away from the pail. Nothing happened. You don't see clothes in the pail. It was only filled with water.

Just when you were wondering how your mother did the trick yesterday, she appeared right behind you, silently. She sternly said:

"What, are you doing."

You were almost shocked to death. You replied:

"Noth..nothing, I was just...pouring powder into the pail...and..."

She interrupted: "for what purpose."

You trembled: "I...just wanted to try...and see..."

She continued with your phrase: "the proper method of washing clothes?"

Oh? that's right! Your mum was washing clothes yesterday!

You were embarrassed by your foolishness, and said:

"Yeah, I was learning how to wash clothes, haha~"

Your mum bended down and spoke to your ear: "Is that so?"

That gave you chills. You realised you have maligned your mum for practising black magic and you immediately apologised. 

Your mum stood up slowly and calmly said: "It's late. Time for bed."

You nodded your head and smiled innocently. She replied you a warm smile and was ready to leave the bathroom.
Right before that, she turned 45 degrees back and said monotonously:

"The magic potion I used yesterday was detergent."

She let out in an evil laughter and left you alone in the bathroom. A lightning stroke across the sky and you dropped the pail of water on the floor.