You already knew that bottled water is hugely wasteful. It’s an estimated 2,000 times more expensive than tap water, it’s more resource-intensive (you know those bottles are made of fossil fuels, right?), and the waste is almost guaranteed to end up in the landfill. But if you need another reason to put down the bottle and turn on the tap, there’s this: Bottled water is actually worse for you than tap water.

That’s right — that $10 bottle could be worse for you than plain old city water.

Doctor Sanaz Majd took on the bottled versus tap issue in the Scientific American podcast House Call Doctor. Majd got interested in this question after her twins were born premature. When she was able to take them home, her doctors recommended that she avoid mixing formula with bottled water. This confused the doctor: Isn’t bottled water better for you than tap?

She started looking into it, and it turns out that while bottled water is regulated by the FDA, tap water is regulated by the EPA and has tighter standards and requirements. The EPA has to disclose the quality of public water, but there’s no such requirement for the FDA. That bottled water you got from the vending machine might have a crystal clear stream on the label, but it could be sourced from a swamp — you’d never know.

Tap water is also treated with chlorine and bottled water mostly isn’t (unless, of course it’s actually city water that’s been bottled, labeled, and then shipped and sold to you at enormous cost, which nearly half of bottled water is). Water that isn’t treated with chlorine can often sit on the shelf (or in your bunker) for months, says Majd, allowing bacteria to grow.

And it’s not just the water itself that could be problematic — it’s also the bottles. You’ve heard of BPA, right? It’s a chemical compound found in many kinds of plastic, and it’s an endocrine disruptor. Animal studies have linked BPA to cancer, diabetes, fertility problems, and behavior disorders — and it leaches into water that’s been sitting in plastic bottles. Drinking lots of it? Probably not great for you.

Now, you may still think that city water is just gross — that you’d rather drink from a bird bath than your own tap. But is anything as gross as bottled water? The answer, if not the water, seems clear.