This is jerry. Hes a common yellow onion, the kind you buy at the grocery store. For some unknown reason, I have become attached, and I would like for him to survive as long as possible.

I have him in some water, but I know that pure water doesnt have enough nutrients to support an onion. I could use dirt, but this is my only measuring cup and filling it with dirt would be suboptimal. I'm also not keen on liquid plant food, because I'm poor and I only need stuff for one onion. Are there household ingredients I can use to keep him healthy?

Tl-dr- how can I nurture this houseplant without dirt or liquid plant food?