The suggestion that people need to drink eight glasses of water per day is a long-held myth. While it’s important to stay hydrated, the amount of water you should consume on a daily basis depends on many different factors, including your age, sex, weight, activity level, and even your location.

A 24-ounce, double-wall insulated smart bottle called the Hydrade can help you figure out exactly how much water your body needs, then send reminders to your phone or other electronic device when it’s time to drink up. It pairs with your phone, health apps, or wearables like the Fitbit or Apple Watch.

Unlike other smart water bottles, though, this one is completely cord- and battery-free. It has a built-in solar panel that lets you charge it naturally when you step outside for a run or hike, and a single charge can power your bottle for up to 20 days. However, it also charges when exposed to any type of illumination—even indoor lighting.

In addition to knowing how much water your body needs, its sensors can also tell whether you’re drinking the water or pouring some out for your dog. The maker, Bazaarian LLC, says the Hydrade Bottle keeps beverages cold for 22 hours, and hot for up to 13 hours.

The bottle is made of dishwasher-safe, BPA-free stainless steel, so it’s eco-friendly and recyclable. There’s a charitable side to the business, too. Depending on your personal level of water intake, Bazaarian will donate a set amount of money to a charity that supports clean water initiatives in developing countries. You can track both your charitable donations and your hydration logs via the app.

Get the Hydrade Bottle on Kickstarter now for $35—a 53 percent discount off of the retail price.