For most Americans, Social Security alone isn't enough to cover their living costs in retirement. So, it's essential to find ways to supplement that income, such as through a pension, taking a part-time job, or buying a rental property. Another option is to invest in dividend-paying stocks, which have the potential to pay a growing stream of passive income. Three worth considering are W.P. Carey (NYSE:WPC), Enbridge (NYSE:ENB), and Brookfield Renewable Partners (NYSE:BEP).

Be a lazy landlord

While investing in real estate is a great way to earn some extra income, it's not passive unless you hire a property manager. That's why real estate investment trusts (REITs) like W.P. Carey can be a great alternative. These entities own and manage a pool of real estate on behalf of investors and distribute the bulk of the income back each quarter, which makes it a truly passive investment. 

A person in a beach chair holding up cash.

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In W.P. Carey's case, it currently pays a 5.9% dividend. Supporting that payout is the stable cash flow generated from its nearly 900 properties that it has leased to more than 200 tenants, which have an average remaining term of almost 10 years. Providing further security to W.P. Carey's dividend is the fact that it only pays out about 76% of its cash flow and it has an investment-grade credit rating backed by low leverage metrics and minimal near-term debt maturities. Meanwhile, W.P. Carey has increased its payout every year since going public by using its retained cash and top-notch balance sheet to acquire properties that expand its cash flow. Those factors make it a top REIT to consider buying.

Pipe some dividend growth into your portfolio

Canadian energy infrastructure giant Enbridge offers investors the best of both worlds. Not only does it pay an attractive dividend that currently yields 4.7% but it expects to grow that payout by a 10% to 12% annual rate through 2024. Supporting the current payment is the company's vast portfolio of fee-based pipelines that generate steady cash flow, as well as the fact that Enbridge has a conservative payout ratio of 50% to 60% of cash flow and an investment-grade balance sheet with improving leverage metrics. Meanwhile, fueling its growth forecast is the 31 billion Canadian dollars' ($24.7 billion) worth of primarily fee-based projects it has underway and the extensive backlog of expansions further down the pipeline.

One thing that's worth noting about Enbridge's future is that the company is slowly pivoting away from oil pipelines and toward renewable energy. While it already has one of the largest wind and solar power generation portfolios in Canada, it has CA$7.4 billion ($5.9 billion) of offshore wind farm projects under development in Europe. These and future renewable investments should enable Enbridge to generate a growing stream of cash flow from more environmentally friendly sources to keep its dividend heading higher even as the world turns toward cleaner power.

An investment in a cleaner future

While Enbridge is slowly building a renewable energy platform, Brookfield Renewable Partners' entire focus is on clean energy. The company is already one of the largest producers of renewable power in the world and is a global leader in hydroelectric power. One of the reasons Brookfield focused on hydro is that these assets generate very predictable cash flow because the company can lock its output up under long-term contracts. Because of those agreements, Brookfield's conservative sub-70% payout ratio, and its investment-grade balance sheet, the company's current yield of 5.6% is on solid ground.

Meanwhile, Brookfield uses its significant free cash flow and balance sheet strength to build and buy additional clean power facilities. The company currently has several wind- and hydro-generating plants under construction and even more under development, which when combined with a few other factors should increase earnings by a 5% to 9% annual clip and power a similar growth rate in distributions to its investors. That combination of a high current payout with steady growth makes Brookfield Renewable Partners an excellent income investment for retirees.

Sustainable income streams that should grow over time

What makes these stocks great options for supplementing Social Security is that the companies generate stable income backed by long-term contracts, which gives them a highly predictable cash flow stream to pay a dividend that's well above average. They further support those payouts with a healthy financial profile, which includes a conservative payout ratio and investment-grade credit. The icing on the cake is that these companies hold back some cash that they use alongside their balance sheet strength to build and buy additional cash flowing assets, which gives them the money to increase their payouts. Add those factors together and this trio should supply a steadily growing income stream to help supplement Social Security.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.