Everyone has to drink water, especially in our hydration-obsessed age, and it’s that fact that has turned bottled water into a multi-billion dollar industry. There are seemingly endless options as you walk down the water channels, from alkaline to minerals to steam distillation, all of which promise to make your body healthier than plain old tap water.

But like many things, the bottled water category is full of marketing hype and bad science, all designed to make you pay for something that can flow freely from the tap in this country. To help swim through this ocean of water advocacy, we reached out to Martin Riese, who was certified as a mineral water sommelier by the German Mineral Water Trade Association in 2010 and now develops full water selection menus for Los Angeles restaurants like Fellow. Below, he shares his basic guidelines for buying the best water to drink.

One caveat: Bottled water is never the most environmentally friendly option, and Riese recommends carrying a reusable water bottle full of filtered water with you as the most sustainable option. But for those unlikely situations, like when you’ve forgotten your bottle and are battling severe dry mouth in an airport terminal, these guides can help you make more sustainable choices that actually taste great.

Consider the source

According to Riese, the brand of water you buy doesn’t actually matter that much. What matters most is where the water comes from, or where it comes from before it’s packaged into those convenient plastic bottles. “When I’m at the grocery store, the first thing I look at is the actual source of the water,” he said. “When it comes from a natural source, like spring water, mineral water or glacier water, that’s what I want to buy.”

Riese tends to avoid brands that bill themselves as “purifying” or “steam distillation,” mainly because they tend to come from public water systems, like water from a tap. “I don’t like the business model, it’s a bit of a scam. They’re filtering everything out of the tap water and maybe adding small amounts of minerals or electrolytes to call it healthy,” he said. “I want my water to come from natural sources designed by nature.”

Don’t be fooled by the marketing hype

As you stroll down the water aisles, each package is stamped with a number of marketing buzzwords like “alkaline” and “electrolytes.” According to Riese, these selling points are almost always marketing hype. There’s no solid research showing that drinking alkaline water or water with a slightly higher pH improves your health, and most “electrolyte water” contains only trace minerals, which water brands insist will keep you healthier and hydrated. “I think the whole bottled water industry is very disorganized in the U.S.,” he said. “60% of the water sold in this country is just glorified tap water, and I think it’s the biggest scam on the planet.”

Think about your personal taste preferences

Although it is often described as “tasteless,” water definitely has flavor. Some waters, like the Texas-born brand Crazy Water, are rich in minerals like zinc, calcium, and silica, each with a certain flavor profile. If you don’t like the salty, sometimes bitter taste of mineral water, consider a brand that uses reverse osmosis filtration, a process that removes up to 99.9% of trace minerals and other contaminants. Keep in mind that most reverse osmosis bottled water, like Aquafina and LIFEWTR, comes from public water systems.

Choose a (more) sustainable package

Because of the inherent environmental impact of bottling and selling water, Riese said, there is no truly perfect water container. He prefers glass because it’s recyclable and because it doesn’t soak chemicals into water like plastic bottles. Aluminum bottles or cans are also a good option because they can be recycled, but many are lined with plastic to prevent anything in the can (like corrosion or rust) from affecting the taste of the water.

Surprisingly, water sold in cartons is one of the least sustainable options for packaging water. “It’s the worst because it looks great from the outside, but the boxes are made of many different layers of materials, including plastic,” Riese said. “A lot of recycling companies can’t even recycle them, so they end up in landfills right away.”