i want to buy a rental income property, what is the lowest downpayment that I make. I am homeowner

On a single family (or single unit), then you will need at least 20% downpayment; on a 2-4 unit property, then you will need at least 25% down (this is assuming you're looking at loan amount for 1 unit under $417k, not the High Balance loans).  You can go as little as 15% down (without any MI, mortgage insurance) with HomePath financing (only on Fannie Mae owned homes) for 1 unit properties.  Hope this helps.  If you need anything else, then don't hesitate to ask.  I'm relatively local for you.