How long will soaked chia seeds last?

Mine are at least 3 or 4 weeks old and seem fine.

I thought the chia seed water/gel would last forever in the fridge because they last forever dry in the cubboard. But No, absolutely not. I didnt go to taste it until about 2-3 weeks (no longer) after making it and putting it in the fridge. I was shocked, spit it out, and felt like vomiting from the smell of it. .. so it probably doesn't last very long.

Have you thought about freezing it? If you wanted to freeze in small silicone molds then you could pop them in a baggie or jar and remove as needed. I put mine in the smallest mason jar I can find when I add the water so mine doesn't go bad in the fridge.

Chia seeds have been known to harbor salmonella, and considering their high fat content, high carbohydrate content, and their physical/chemical reaction to being soaked in water, they are an ideal growing medium for any number of hazards.

The USDA does not have a published opinion on the topic.

The EFSA has approved them as an ingredient in all forms,including uncooked, but has only researched cooked form (which is typical for seeds and nuts)

Give the lack of guidence from a credible organization, and the wildly varying ranges of unauthoritative sources, I would treat soaked chia seeds as most akin to leftovers of a salad that has dressing applied, which is to say even in the refrigerator, no more than a day and "when in doubt throw it out".

You can do a test to determine it like this. The next time you get to-go food, ask for 3-4 little sauce cups. Make your chia gel, date the cups, put 1/2 tsp in each cup, and store them in the fridge. Test one cup at a time every 3-4 days. Timings can vary because every fridge's temp is different, though the middle shelf is usually the coldest.