2026–2027 · Division B · Device + written

Water Quality

Build and calibrate a salinometer alongside marine and estuary study.

Calibration · measurement · uncertainty

Plan for: a supervised wet-work station

2027 · Know before you build

Rules & required-items check

A practical checklist for students, parents and coaches, written from the 2027 Division B manual. Each note points to its source rule.

Get the official manual

1–10% mass/volume

Build and calibrate for the full salinity range.

Rule 3.IV.a

400–600 mL beaker

The instrument must work with at least 400 mL of solution inside it.

Rule 3.IV.b

Category C eyewear

Required during the salinometer test.

Rule 2.e

10% device component

Bringing the device and measuring accurately are worth 5% each.

Rule 4.a.ii–iii

Source: printed pages B59–B60 · PDF pages 64–65 · Checked September 13, 2026 (manual); October 25, 2026 (published corrections)

Your team’s packing list

One student-built salinometer
Build, calibrate and bring one salinometer/hydrometer that both partners can demonstrate. Bring Category C eye protection for testing.
2027 rule 2.d–e; 3.IV.a
One reference sheet
One 8.5 × 11 inch sheet per team may have information on both sides. Lamination or a sheet protector is allowed; attached labels and extra sheets are not.
2027 rule 2.c
Writing tools and calculators
Writing utensils and up to two Class II calculators are allowed. Laptops, tablets and similar computing devices cannot be used in competition.
2027 rule 2.a–b; 3.IV.a

At the competition station

Test sample and vessel
Design for the specified 400–600 mL beaker holding at least 400 mL of saltwater. The testing arrangement follows Part IV; calibration solutions are at the supervisor's discretion, so arrive with an already calibrated device.
2027 rule 3.IV.b–c

Build to these limits

Calibrate the correct concentration
The range is 1–10% mass/volume, not mass/mass or practical salinity units. In mass/volume percent, a 5% reference contains 5 g of solute per 100 mL of final solution.
2027 rule 3.IV.a; concentration-unit explanation

Fit the vessel, not an arbitrary size limit
There is no separate device dimension cap. It must operate inside the specified beaker with the required volume; test clearance and readability during calibration.
2027 rule 3.IV.b

Simple electronics are allowed
An electronic salinometer is permitted, but it cannot be programmable or capable of Wi-Fi communication. A simple hydrometer remains an option.
2027 rule 3.IV.a

Rehearse competition dayTiming, setup and what happens during a scored attempt

Report to a tenth of a percent
Read the unknown with your own calibrated device and report salinity to the nearest 0.1%. The printed full-credit tolerance is ±1% at Regionals and ±0.5% at States/Nationals; see the scoring clarification below.
2027 rule 3.IV.c
Prepare for marine and estuary science
The remaining 90% is split equally among ecology, coral-reef organism identification/ecology, and water-monitoring data analysis. Identification requires common names and the specified organism list.
2027 rule 3.I–III
Separate device testing from data questions
Water-monitoring questions cover salinity, pH, nutrients, turbidity, oxygen, temperature, fecal coliform, solids, oxygen demand and aragonite saturation. Part III does not involve performing physical lab tests.
2027 rule 3.III

Understand the scoreWhat earns points, what loses them and how teams rank

Keep both device opportunities
Five percent of the event score is for bringing the salinometer for testing; another five percent is for an accurate measurement. Written/identification sections each contribute 30%.
2027 rule 3.I–IV; 4.a
Higher total wins
Selected test questions break ties. A strong device alone cannot replace preparation for the other three sections.
2027 rule 4.a–b

Confirm with your coach or tournament host

Clarify tolerance interpretation
Part IV.c prints ±1% and ±0.5% without explicitly distinguishing percentage-point error from relative percent error. Ask the supervisor which interpretation the scoring sheet uses; this guide does not silently choose one.
2027 rule 3.IV.c
Check event-day logistics
Confirm sample vessels, whether calibration solutions are offered, and the testing sequence. The supplied event pages do not specify an impound requirement.
2027 rule 1–2; 3.IV.b–c

Use these preparation notes alongside the authoritative manual, its diagrams, current corrections and the host’s instructions. They are not a complete rule replacement or a certification of your device. Both partners should be able to explain their design and operate it independently.

September 22 national corrections resolve the glider flight period to six minutes and correct Water Quality organism spellings (Phaeophyta, Eucidaris, Octocorallia). October 12 Scrambler kit guidance and form are linked below. Recheck national clarifications and tournament instructions before competition.

Rules corrections Official clarifications Safety & building policies

Kits, stock & delivery

Public seller pages checked October 27, 2026. This is a dated snapshot, not live stock. Prices are advertised USD before shipping/tax; confirm the single-kit option and delivery before paying. An add-to-cart button alone does not establish stock. Kits still need student assembly, testing and rules checks.

No complete ready-to-ship student-built salinometer kit was verified. A broad water-quality lab kit is unnecessary for this build. Use the official straw/clay or pipette plan below; most parts can come from school or home. No supplier delivery date is claimed for household parts.

Build your own

A prototype you can make and improve

Original club build suggestions. Pair these steps with the rule checklist above; they are not an official design or a guarantee of competition compliance.

Parts to gather or borrow

Make two trial floats: two narrow drinking straws (or disposable plastic transfer pipettes), a small amount of non-hardening oil-based modeling clay for sealing/ballast, waterproof fine marker and tape. Avoid water-soluble or air-drying clay. Do not buy a finished commercial hydrometer as the student-built device.
Calibration supplies: table salt, distilled water, balance, a vessel that measures final solution volume, labeled storage cups/bottles and a 400–600 mL beaker. Borrow school lab equipment rather than purchasing a broad activity kit.
Category C splash goggles for the salinometer test. A rack or 3D printer is optional bench equipment, not required for the float.

Starter plan: dimensions and assembly

Follow the illustrated official salinometer PDF linked below. Seal a straw’s lower end with clay, or seal/ballast a plastic pipette. Add only enough ballast for upright floating. Choose the stem length experimentally so the device floats freely with at least 400 mL in the specified beaker, without touching bottom or walls.
Prepare a calibration ladder at 0%, 1%, 3%, 5%, 7% and 10% mass/volume. For each 500 mL final solution, use respectively 0, 5, 15, 25, 35 and 50 g of salt. Dissolve in less than 500 mL water, then bring the FINAL solution volume to 500 mL; do not add 500 mL water to the salt.
At consistent temperature, place the float in each standard, let it settle, and mark the liquid level with concentration. Read the same part of the meniscus each time. Record a calibration chart; do not assume equal spacing between concentration marks.
Have a partner make a blind sample, read it to the nearest 0.1%, then compare with the known value. If marks are crowded, try a narrower stem and recalibrate. Any change to ballast, seal, tape or stem requires a new calibration.

Before calling it ready

Check the full 1–10% range, free flotation, dry readable marks and seal integrity over repeated trials. Test in the required vessel with at least 400 mL, not just a tall narrow home jar.
Keep the device student built and explain buoyancy and calibration. Programmable or Wi-Fi electronics are prohibited; the straw design needs no electronics. Copy needed calibration information onto the permitted single two-sided reference sheet.

3D printing & design files

A student-designed sealed hydrometer body is a possible approach under the open device-material rules; it must fit the beaker, float freely and be calibrated after printing and sealing. Layer leaks and inconsistent mass can ruin calibration. A straw or pipette is the simpler starting point. Electronics cannot have programmable parts or Wi-Fi. A verified calibration-sample rack STL is listed below for bench organization only. No usable passive printed-float download has been verified.

There is no blanket approval of all printed parts. The event’s specific material and construction restrictions take priority. Students should retain file source, license, CAD changes, print settings and test results, and build and explain their own device. Ask an official clarification when a design’s legality is uncertain.

The national general FAQ recognizes modeling a 3D-printed component as part of student design and construction. That answer does not waive an event’s material requirements. Read the national FAQ (opens in a new tab).

Official student-building and mentoring policy

Downloadable 3D files & 2027 use

Model review: October 27, 2026. Separate from the kit-stock review. File access and contents were checked; no physical print, load test or tournament approval is implied.

A verified printable sample rack can organize calibration practice. It is not a salinometer and earns no device points by itself. No usable passive printed-float download was verified. Humidity hygrometers and programmable/Wi-Fi brewing instruments are not substitutes for the required student-built salinity device.

Use the creator’s Files tab or the exact file link below. If a raw STL/STEP opens as text, use Save link as and retain the listed extension. STEP needs CAD export to STL first. For OpenSCAD source, retain included dependencies, render the main part files and export STL. STL has no unit metadata: confirm millimeters in your slicer. Slice the model for your own printer; do not run someone else’s G-code.

Verified file access · Calibration bench only

Calibration-sample test-tube rack

By Frank Markesteijn · Binary STL · 2,262,084 bytes

Test-tube-rack-E8Z-Z-high-18mm-4x6.stl

What you can adapt: Use as a bench organizer for appropriately sized, labeled tubes of known calibration solution. Test tube fit before filling and keep the rack in a spill tray. This 18 mm / 4 × 6 rack is for sample storage; it is not a holder for the event’s much larger testing beaker.
2027 restrictions & required changes: Practice aid only: the rack does not replace the student-built, calibrated salinometer or demonstrate measurement accuracy. Prepare 1–10% mass/volume standards in accurate volumetric equipment, not by measuring inside printed cavities. Test the actual device in the specified 400–600 mL beaker with at least 400 mL of solution; the float must move freely, without wall/bottom contact or support from a rack. Report to 0.1%. Any electronic salinometer must be nonprogrammable and incapable of Wi-Fi communication. Calibration solutions at competition are discretionary, so do not assume the rack, stored samples or extra equipment may be used there. Retain the permitted reference-sheet/calculator limits and Category C eyewear for device testing.; Rule checkpoints: Water Quality 2.a–e; 3.IV.a–c. Calibration-bench organizer only; follow the official straw/pipette build guide for the actual measuring device.
License & attribution: CC BY-SA 4.0, released by the uploader as their own work. Credit Frank Markesteijn, identify changes and share distributed adaptations under the same or a compatible license.

Verification: Downloaded the actual STL; validated its 45,240-triangle binary length. SHA-1 matches the checksum on the uploader’s file page: 8d85b0dd9faf4e8fd19b166b9beddf5ad2f57f42. Fit, stability and physical printing have not been tested.

Download calibration-sample rack STL Creator & instructions License source

Verified plans, videos & tutorials

Links were read directly or confirmed on the national event page. Video playback, vendor checkout and downloadable model fabrication have not been tested. Historical resources are labeled; an older video cannot set 2027 dimensions.

Official making and using a salinometer handout (PDF)

Illustrated straw/clay and pipette approaches, calibration and buoyancy background. Follow the current manual where background wording differs.

Plan your practice kit

Suggested supplies, not a mandatory shopping list. Borrow shared equipment first; confirm every competition item against the rules before purchasing.

Prototype supplies

Rules-compatible salinometer body, ballast and scale materials
Salt and water for coach-prepared calibration solutions

Shared tools

Balance, measuring vessel and thermometer for practice
Labeled sample containers and a spill tray

Storage & records

Protective device case and a calibration chart
Waterproof labels, notebook and cleanup supplies

Your first practice

Make one useful comparison.

1
Confirm the device rules before choosing construction materials.
2
Calibrate with known solutions and record the temperature and preparation method.
3
Use a separate unknown sample to check measurement error without seeing its value first.

Build a record you can learn from

Keep every trial, including failures. Record the conditions, one changed variable, what happened and the next decision.

• Reference salinity and units
• Device reading and units
• Temperature (°C)
• Error / repeatability / calibration revision

Download blank test log

Original club CSV template. Save it in your team’s approved workspace and share it with your coach. It does not upload or sync to student progress, and it does not replace any required official log.

A role for everyone

Students

Own the design decisions. Keep a revision record, learn the relevant rules and be ready to explain how your device works and why you changed it.

Parents

Help label supplies and protect the instrument. Keep practice solutions separate from food and follow the coach’s preparation and cleanup plan.

Coaches

Verify calibration preparation and measurement units, then use blind samples. Device skill and written knowledge need separate evidence.

Resources for your next step

Official Water Quality resource page

Official event resources include salinometer preparation. Check current marine/estuary scope and device requirements in the 2027 manual.

Official webinars & event workshops

Find coaching sessions and recordings. Check each resource’s event, division and season.

Open Water Quality written practice