How To Test HOW TO TEST YOUR WATER The best time to take a rain sample is in the initial stages of a developing rain storm. A migrating low pressure system is best as apposed to an isolated convective cell such as a thunderstorm. Try to collect the sample from the very beginning of the rain event. Metals testing is not typically expensive, Basic Lab. in Redding California charges 21 dollars per element. RAIN AND SNOW Any clean glass or plastic container can suffice for the collection of a rain sample, try to gather about 8 ounces of rainwater or