Some water testing packages include instructions that recommend that you collect your water sample using both the first draw and fully-flushed collection methods. Here's how to do so properly:
Remember: always use a low flow when collecting the sample and do not overflow, as some containers include a small amount of preservative.
1) Begin By Collecting the First Draw Sample
When: Most people choose to collect a first draw sample first thing in the morning, after water has been stagnant in the plumbing overnight (at least 6 hours). Ideally, no water should be run at any tap, toilet, shower etc on the premises during that 6 hour period.
Why: Water in a first draw sample will have had time to interact with the plumbing and may reveal any issues related to the pipes such as leaching metals.
How: As soon as water flows from the tap, begin filling the sample container with a low, gentle flow according to any specifications listed on the instructions.
2) Next, Collect the Fully-flushed Sample
When: After having collected the first draw sample, you can then prepare to take a fully-flushed sample. To flush the pipes of any standing water, run the tap for about 5 minutes to clear the waterline.
Why: A fully-flushed sample will likely be able to capture the more volatile compounds that can dissipate in to the air quickly.
How: After having flushed the water line for about 5 minutes, adjust the stream to a low, gentle flow according to any specifications listed on the instructions.