Stainless steel water bottles are generally considered a safe and non-toxic option. 

However, if you have concerns about the quality or safety of your thermos bottle, here are some ways to test it:

1.Check for Rust or Corrosion: Examine the inside and outside of the stainless steel vacuum flask for any signs of rust or corrosion, 

which could indicate that the stainless steel is not high-quality or has been exposed to water for extended periods of time. 

If you see any rust or corrosion, it is best to stop using the insulated water bottles.

2.Fill with Hot Water: Fill the stainless steel tumbler with hot water and let it sit for a few hours. 

Then, touch the outside of the sports bottle to see if it has become too hot to hold. 

If the water bottle stainless steel is too hot to hold, it may not be well-insulated, which can cause the bottle to leach chemicals into the liquid.

3.Smell and Taste Test: Fill the hot water bottles with water and let it sit for a while, then smell and taste the water. 

If the water has a metallic taste or smell, it may indicate that the stainless steel is of poor quality or that it has been contaminated with other metals.

3.Research the Brand: Research the brand of the reusable water bottles to see if they have a good reputation for producing safe and high-quality products. 

Look for reviews and ratings from other customers to see what their experiences have been like.

Fayren Stainless Steel Water Bottle - This is a high-quality water bottle that is made of stainless steel and is BPA-free. It has a durable construction and comes in a variety of sizes and colors.

By following these tips, you can help ensure that your double wall insulated stainless steel water bottle is safe and of good quality.