We’re all awed when celebrities donate millions of dollars to worthy causes. And we’d all probably like to volunteer more than we do. But most of us have full-time jobs with modest incomes—or a full-time college schedule with no income—which make it hard to make a difference. Here are 3 ways to improve the world when you don't have a lot of money or free time.

1. Donate blood.

Every year, 4.5 million Americans need blood transfusions. Every day, 40,000 pints of blood are used to save the lives of cancer patients, accident and burn victims, newborn babies, and others in need. And statistically, someone is in need every two seconds.

Donating blood is a fast procedure; having the blood extracted takes less than 15 minutes, and the entire process, including paperwork and refreshments, is done in around an hour. It’s also safe. There is no risk of infection through the needles, because they’re sterile and only used for one donor before being discarded.

Yet of the 38 percent of Americans eligible to donate blood, only around 10 percent actually do. Among non-donors, 17 percent have never donated because they’ve “never thought about it” and 15 percent say they’re too busy to donate. But if one percent more Americans donated, blood shortages would be eliminated.

Lots of schools, universities, places of worship, and companies host blood drives. By finding one and taking an hour to donate one of the ten pints of blood in your body, you could save as many as three lives.

2. Sign up to be an organ donor.

As of August 2017, 116,000 people were waiting for organs in the U.S. Every day, 20 people die before getting the organ they needed. And every 10 minutes, another person joins the waiting list.

And while 95 percent of adults say they support organ donation, only 54 percent have actually signed up to donate. Some people worry that if an organ donor is in a life-threatening situation, doctors will let him or her die to get access to more organs. Others assume organ donations would make it impossible for them to have an open-casket funeral. Still others believe they’re too old or too ill to have viable organs.

But these are myths. Almost anyone can donate. And even if your organs are deemed unusable after your death, it still makes sense to register, just in case.

After all, by donating, you can save up to eight lives.

3. Drink from a reusable water bottle.

In the United States, buying plastic water bottles, using them once, and then disposing of them is a common practice. In fact, worldwide, people are buying 1 million water bottles per minute.

91 percent of those bottles are not recycled. And it takes 400 years for plastic to decompose, so in the meantime, it collects in landfills and the oceans. Which means we’re on track to have an estimated 12 billion metric tons of plastic in landfills by 2050—the same year we're predicted to have more plastic than fish in the oceans.

And frankly, these devastating environmental consequences aren’t worth it. Neither is the monetary cost of buying water. The world spends around $100 billion on bottled water every year, and in developed countries with ready access to sanitary tap water, this is an unnecessary expense.

The National Resources Defense Council has found enough contaminants in bottled water to conclude that it is not necessarily cleaner or safer than tap water. And despite what the bottled water industry wants you to think, in 2009, Food and Water Watch reported that 47.8 percent of bottled water comes from tap water anyway.

Invest in a reusable water bottle. Save the world and your wallet.

Ultimately, improving the world doesn't have to be time-consuming or expensive. If we all take small actions, we can create big change.