Review on Copper Test Kit: Accurate 90-Test Aquarium Water Testing with API by Diane Haney

So if you're buying this to test your tap water for safety standards it works pretty well but it's a color test and it's hard to tell and very subjective what reading is. So you're really just guessing and are accurate to within 1.0ppm. The thing is, there are digital testers on the market that will give you 0-5ppm with an accuracy of 0.01ppm for as little as $50. However, it's good for the price.