Usually the minimum down payment requirements for a rental property is 20%.  Now this really does depend on whether the property will also be your primary residence, so that can actually go down if it is your primary residence.

You will need to prove where they down payment for your purchase of a rental property is coming from. This might be from money sitting in your account, a secured line of credit, Mutual funds, stocks, or money in corporations.  In most cases you will need to show proof where these funds are coming from.

In some cases, you might have to show that the funds have been in your account for at least 90 days. This can be particularly problematic if you are recieving funds from a joint venture partner that is not going to qualify for the mortgage, and will not be on title.  This may require the investor to close the deals with their own funds, and then bring in the joint venture partner after the transaction has closed, and use the funds to replay the investor.

Where is your down payment coming from for your next purchase?  Make sure that you focus on your next deal and not the growth of your entire portfolio for now.  Make a plan to ensure that your funds are reading to go for the next property that you would like to purchase.