Will my Criminal conviction hurt my application?

Hello,
I'm applying for a Spousal Visa for the UK. My partener and I fulfil all criteria.
I am worried that a criminal conviction could hurt my application. The police report that I currently have does not state the nature of the crime, but just lists it as "Domestic Assault" with $300( (Australian $) fine.

I want to know if it would help to add an explanatory note: I recieved the conviction allthough I did not infact assault anyone. I threw a cup of water (not the cup) at a tenant in my home, who refused to leave after he had been given notice and his time had expired. The water didn't even touch him but he went to the police and pressed charges. I admitted to throwing the water where upon I was arrested and convicted. The police were apologetic and said that it was a technicality but that the were required by law to press the charges.

Should I add this to the cover letter of my visa application or just provide the document from the police or supply a transcript of the actual interview that was conducted when I was arrested?

Thanks, in advance for your advice.