Down the channel until it seats
Slide the flashlight down the angled channel, head first, until it seats against the round housing. The channel sets the angle, so there's nothing to aim.
Low batteries make a real sample read as clean, and the beam still looks fine when they're low. If it worked before and then stopped, swap them.
Unwrap the digital microscope and press the power button. Drop it into the round housing, screen up, so the lens looks down at the light. Leave the wand aside until you have a filter to read.
Fill the jar almost to the top with the water you're testing. It holds about 100 mL (3.5 oz). Leave room for the 1 mL vial you add next. Results are reported per 100 mL, so use the full jar.
Add the vial, swirl gently, and wait 15–20 minutes. Longer is better; the dye needs time to bind.
Cover the jar while you wait. Dust from the air lands in an open jar and gets counted.
Open the holder, drop the filter in, twist it shut
Unscrew the holder, set the round filter membrane inside, and screw it back together.
Twist the holder onto the syringe tip until snug
Twist the assembled filter holder onto the syringe tip until it's snug.
Pour the prepared water into the top of the syringe.
If you have a 60 mL syringe, fill and push it roughly twice. If you have a 100 mL syringe, fill and push it once. Either way, keep going until the jar is empty so the full 100 mL sample passes through the same filter.
Unscrew the filter holder before you pull the plunger back for the second fill. Pulling against the filter can damage it.
Push the water through right away; don't let it sit.
Unscrew the holder and take out the filter. Keep the side that faced the water pointing up. That's the side you read.
Use the tweezers to place the filter flat on a clean paper towel, keeping the side that faced the water pointing up. Let the towel absorb the excess water until the filter is slightly damp. Keep the top uncovered and lift it by the edge before it dries completely and curls.
With the tweezers, lay the filter flat on the wand, collection side up. Slide the wand into the rig until the filter sits under the microscope and over the light. A curled disc throws shadows that read as empty filter, so get it flat.
Keep the filter slightly damp so it lies flat, with the collection side facing up.
Move the wand around under the microscope to hunt for microplastic particles
Switch on the microscope. The lens sees a small patch at a time and the particles are scattered, so move the wand in and out and side to side until you have covered the whole disc. Go slow and overlap your passes.
Each faint glowing dot or short fiber is a suspected microplastic. Count them as you go. The color varies with the lens and the light — more red or less red is fine. Compare against the examples below.
Your count is a floor. The membrane is 1 µm, so anything smaller passes straight through, and the included microscope only sees particles down to about 5 µm. For every particle you can see, there are more you can't.
Instructions
One sample at a time. Most of the 30 minutes is waiting after you add the vial.
Three parts. Tap one to open it.
Slide the flashlight down the angled channel, head first, until it seats against the round housing. The channel sets the angle, so there's nothing to aim.
Low batteries make a real sample read as clean, and the beam still looks fine when they're low. If it worked before and then stopped, swap them.
Unwrap the digital microscope and press the power button. Drop it into the round housing, screen up, so the lens looks down at the light. Leave the wand aside until you have a filter to read.
Fill the jar almost to the top with the water you're testing. It holds about 100 mL (3.5 oz). Leave room for the 1 mL vial you add next. Results are reported per 100 mL, so use the full jar.
Add the vial, swirl gently, and wait 15–20 minutes. Longer is better; the dye needs time to bind.
Cover the jar while you wait. Dust from the air lands in an open jar and gets counted.
Unscrew the holder, set the round filter membrane inside, and screw it back together.
Twist the assembled filter holder onto the syringe tip until it's snug.
Pour the prepared water into the top of the syringe.
If you have a 60 mL syringe, fill and push it roughly twice. If you have a 100 mL syringe, fill and push it once. Either way, keep going until the jar is empty so the full 100 mL sample passes through the same filter.
Unscrew the filter holder before you pull the plunger back for the second fill. Pulling against the filter can damage it.
Push the water through right away; don't let it sit.
Unscrew the holder and take out the filter. Keep the side that faced the water pointing up. That's the side you read.
Use the tweezers to place the filter flat on a clean paper towel, keeping the side that faced the water pointing up. Let the towel absorb the excess water until the filter is slightly damp. Keep the top uncovered and lift it by the edge before it dries completely and curls.
With the tweezers, lay the filter flat on the wand, collection side up. Slide the wand into the rig until the filter sits under the microscope and over the light. A curled disc throws shadows that read as empty filter, so get it flat.
Keep the filter slightly damp so it lies flat, with the collection side facing up.
Switch on the microscope. The lens sees a small patch at a time and the particles are scattered, so move the wand in and out and side to side until you have covered the whole disc. Go slow and overlap your passes.
Each faint glowing dot or short fiber is a suspected microplastic. Count them as you go. The color varies with the lens and the light — more red or less red is fine. Compare against the examples below.
Your count is a floor. The membrane is 1 µm, so anything smaller passes straight through, and the included microscope only sees particles down to about 5 µm. For every particle you can see, there are more you can't.
These details can make particles harder to see. If the screen looks unusual, check both before reading the result.
If the 25 mm filter disc curls or buckles, the light can hit it unevenly and create darker areas. Handle it with the tweezers and try to keep it very flat while you read it.
Place it on a paper towel, collection side up, until it is slightly damp. Damp makes the disc stick flat; bone-dry, it curls.
The flashlight is fixed in place, so aiming isn't the problem — the batteries are. Below about 50–70% charge the blue light stops exciting the dye and nothing glows, even with plastic on the filter. You won't see it happen: a half-dead cell still throws a beam that looks bright. If the kit was finding particles and then stopped, put in fresh batteries before you trust a clean result.
Have two tests? Run one on unfiltered tap water and one after your filter.
Wash the jar thoroughly. Don't drink from it.
Suspected microplastics can appear as small glowing dots, fibers, or dark marks. Use these views as a reference while reading the filter.
The color varies with the lens and the light: deep red, warm orange, or almost blue. Every view below counts. Each arrow points at one thing to count.
What you're looking at
A long fiber may be polyester, or it may be cotton or rayon, which aren't plastics, or a clothing fiber that landed from the air while your sample sat open.
Carbon shed by a carbon filter, grit, rust and other debris all look like black specks at 10x, the same as black plastic. Looking at one doesn't tell you which it is. More on this.
Glowing particles are counted as likely microplastics. Some non-plastic material, like certain organic matter, can also fluoresce, so your count is a screening estimate, not a lab-confirmed identification. Black plastics such as tire wear often don't take up the dye and can look dark instead of glowing. Sand and sediment show up as non-glowing grains with 3D texture; don't count them.
The filter captures particles down to 1 µm. The included microscope sees particles down to about 5 µm, so smaller particles on the filter won't show up and your count is a floor. Limitations.
These images do not show any microplastics. An even view with no distinct glowing dots — nothing to count.
Each refill covers one more run — keep the microscope, syringe, and filter holder you already have. sold separately.
Short answers to what people ask us mid-test. Type a word to filter the list.
The step-by-step instructions are online at thewatertest.com/instructions. You can also open them using the Start your test button in your delivery email. Start with Part 1: Test the water, then follow Part 2 for the microscope walkthrough.
Start with the bottom of the microscope's clear plastic cap about 3 inches above the filter. A little closer or farther is fine; adjust the focus until the filter surface looks sharp on the screen. You don't need digital zoom, and you should move the wand to inspect the whole filter.
No. Normal room lighting is fine. Keep the microscope's built-in white light completely off and use the blue flashlight to illuminate the filter.
Excess water can create reflections: place the filter on a clean paper towel, collection side up, and let the towel absorb the water until the filter is slightly damp. Lay it flat, focus on the filter surface, and check that the microscope's white light is off and the blue flashlight has fresh batteries. Shiny reflections and dark spots alone don't indicate microplastics; look for glowing dots or short fibers and compare them with the example images on this page.
Leave it in place and wipe it with a microfiber cloth, the same way you'd clean glasses. Anything on the glass is only in your view, not on the filter, so it doesn't change the count.
Run it through the dishwasher. Don't drink from it.
Yes. Foil, a lid, or a plate on top all work, and covering it keeps dust out.
Don't force it. Pull the plunger back, unscrew the filter holder, reseat the filter so it sits flat, screw it back on, and push again gently and steadily. The full push should take 20 to 30 seconds.
Yes. Set it flat on a clean paper towel with the collection side facing up and let the towel absorb the excess water until it is slightly damp. Adding more water can create reflections; lift the filter by its edge before it dries completely and curls.
Glowing dots and short fibers can be faint as well as bright. Focus on the filter surface and compare with the example images on this page; brightness alone doesn't identify the material. Count suspected microplastics that glow under the blue light, including faint ones, while keeping the microscope's white light off.
That's a fiber. A glowing fiber is often plastic, such as polyester or nylon from clothing, though some natural fibers can also pick up the stain. Count it as one particle.
You can see the big bright ones by eye under the blue light, but you'll miss most of the small ones. Use the microscope for the count.
A stray fiber or two from the air or your clothes can land on the filter, and that won't change the overall picture. Keep the filter covered when you're not looking at it. Touching it after the dye has worked doesn't add stain.
First turn the microscope's white light completely off, use fresh batteries in the blue flashlight, and focus on the flat, slightly damp filter. Move the wand slowly to inspect the whole disc. If you still see no glowing dots or fibers, record no suspected microplastics observed in this sample; the kit cannot establish that the water is free of microplastics.
Most people find suspected microplastics when testing unfiltered tap water or bottled water, but a sample can show no visible glowing particles. If you see none, check the lighting, flashlight batteries, focus, and filter flatness, then search the whole disc. A zero count applies to what you observed in that sample within the kit's detection limits.
No. Turn it all the way down until it is completely off. The blue flashlight is the only light the filter should get.
Normal. The tint varies from deep red to orange depending on the light and the filter. Particles still show up as bright dots on top of it.
About 24 hours. No need to rush to the microscope.
Stuck on a step? Use the chat in the bottom-right corner.
Have the current kit? Open the current instructions.