I used a field colorimeter in bio. Allow me to convince you to go a different route.
Ultimately, you want to know what’s in your water. Sampling water right out of your tap will tell you what you want to add to support your plant, but it won’t help you remove any problematic components.
Instead of starting with testing, why not start with a reverse osmosis filter? For a fraction of the price of that colorimeter you could have water that’s completely free of toxic heavy metals. From there you can use preventative amendments to put plant available nutrients back into the water.
If you were to focus on filtering, you’d save money and get to “clean” water, which is ultimately your goal. Am I making sense?