When obtaining a water sample from the faucet, be sure that no contaminants are introduced by mistake. In some cases, contaminants have shown up in water tests that didn't actually come from the water itself.
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Clean the screen inside your faucet, and let the water run for a few seconds. Peel off the sanitary sticker and remove the cap close to the water source. Do not place the cap on the counter or anywhere else, and do not turn the cap with the open side up, as this can capture contaminants that will affect your water test. When the sample bottle is full, replace the cap, again with a minimum of movement. This will ensure that your water test will read accurately.