Erin Brockovich ? the activist icon whose life was captured by Julia Roberts' Oscar-winning performance ? is known for being a gutsy truth-teller.

In an exclusive interview with PEOPLE, the consumer advocate gets candid about her struggles with dyslexia and how she handles doubters. She explains how these challenges continue to fuel her activism and her first book about the water crisis, Superman's Not Coming : Our National Water Crisis and What We the People Can Do About It .

"It was difficult for me to look back on my own moment of sharing my dyslexia," Brockovich, 60, says of the struggles of writing the book, "And how much I felt suppressed, or oppressed, with a learning disability, how I became labeled, how I see that happening in other communities."

In Superman's Not Coming , Brockovich writes that her dyslexia impacted her reading comprehension and her grades. Only with the support of a friendly teacher, who recognized how smart she was, and her parents' encouragement did the young girl regain confidence in herself ? and learn the importance of persistence (or "stick-to-itiveness," as her parents would say).

"My mom and dad, the greatest gift they gave me was being honest with myself, being accountable," Brockovich says. "It's okay if you make a mistake. Owning it. My dad wasn't big on lying. And my mom, [she taught me] you've got to have that gumption, and when the going gets tough, you've got to get going."

The young legal clerk needed all of these lessons when she helped the residents of Hinkley, Calif. ? who were dealing with life-altering effects of water contamination ? reach a $333 million, class-action settlement with PG&E in 1996, one of the biggest of all time. Brockovich continued on with her work as an activist and started receiving a flood of emails from concerned citizens after the 2000 Erin Brockovich film made her a household name. The emails persist to this day.

"I remember going to watch the film by myself and listening to comments as people walked out of the theater," she remembers. "[They said,] 'I could do that.' 'Well, I wonder if our water is okay.' 'I wonder if that would happen to us. Maybe it already is us.'"

Brockovich has been on the warpath fighting not only water contamination, but other problematic developments that impact vulnerable communities, like dangerous medical devices, for the past 24 years. Surprisingly, she continues to get doubters, despite her success in pushing for change.

While advocating on the behalf of the citizens of Columbia, Missouri, who were dealing with issues tied to chloramine, Brockovich battled it out with a scientist on a radio show.

"Here was a scientist on who said, 'Come on, Erin. Be honest. You don't have all the data to conclude that this chemical in the water and what we're doing is in fact harming these people,'" Brockovich remembers. "First of all, you are correct. I don't have all the data and I'm willing to own that. But here is what you're not seeing on your side of the science: You don't have all the data either to conclude that it doesn't hurt those people."

Brockovich urges people to continue to fight for what they believe in ? even if they don't have a science degree. She says that people who attack or try to cast doubt often have something to hide.

"I tell people all the time: The minute you run into that person who starts taking you down and starts throwing those barbs at you, and starts that gaslighting moment, that is the minute I'm watching you," she says. "Because there is a reason why you need to throttle me back in hopes I don't find out what you're doing."

Brockovich's belief in individual activism ? rather than relying on leaders, corporations or the government to handle the water crisis ? is the guiding theme in her new book. The United States and the world is at a "tipping point" with the water crisis and it's time to act, she says.

"I want us to understand the importance of water," Brockovich says. "I think that we do, but I don't know that we understand the tipping point that we're at, and what we can do in our own towns to empower ourselves so we have safer water."

Superman's Not Coming uses both real communities and startling facts to show how devastating the water situation really is. Brockovich writes about "fraudulent science" hiding the problems, the situation with PG&E as well as the inspirational individuals and communities who decided to take a stand.

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Brockovich is proud to work with community members, from Hinkley, Calif. to Hannibal, Mo., to push for change.

"Hinkley changed my life on such a personal level," the consumer advocate says. "I don't know that I believed [in myself], but they believed in me, and then I believed in them, and it became this mutual admiration where we were there for each other."

Many of the first people to say something about community problems are mothers, she says. And like these mothers-turned activists, people shouldn't wait for the government or corporations to do the right thing.

"The hope is when people know better, they do better and they rise up," Brockovich says. "We can turn that tide. I'm going to believe that until the day I die."

Superman's Not Coming is on sale now.