Create a Mini Water Filter
Lesson preview: the Mini Lesson and Vocabulary are open to everyone. Guided practice, exercises, the parent checklist and the printable PDF worksheet come with full access (free 7-day trial or membership).
What you will learn
- 1Explain what filtration is and how it separates mixtures by particle size
- 2Describe the layers of a water filter and the role of each material
- 3Distinguish between pure water and impure water
- 4Identify water as a solvent in solutions
Mini Lesson
Water found in nature is rarely pure — it carries tiny particles of soil, sand, and other substances. Filtration is a physical separation method that removes solid particles from a liquid by passing the mixture through a filter medium. The filter allows the liquid and very small dissolved particles to pass through while trapping larger solid particles.
Mixtures and Solutions
- A mixture is formed when two or more substances are combined but NOT chemically joined — each keeps its own properties.
- A solution is a special mixture where one substance (the solute) dissolves completely into another (the solvent). Water is the most common solvent.
- Muddy water is a mixture: the soil particles do NOT dissolve — they float or sink.
- Salt water is a solution: the salt dissolves completely and cannot be seen.
- Filtration can separate a mixture (e.g. muddy water) but cannot separate a solution (e.g. salt water).
How a Water Filter Works
A simple water filter uses layers of materials with different particle sizes to trap impurities. Water flows downward through each layer, leaving larger and then smaller particles behind.
- Cotton (top layer) — traps the largest particles such as leaves and large debris.
- Charcoal (second layer) — absorbs chemicals, odors, and very fine particles.
- Sand (third layer) — traps sediment (bits of soil that settle at the bottom) and smaller particles.
- Gravel (bottom layer) — supports the layers above and keeps the sand from washing out.
Pure vs Impure Water
- Pure water contains only H2O molecules — no dissolved minerals, gases, or particles.
- Impure water (tap water, river water, seawater) contains dissolved salts, minerals, gases, or suspended particles.
- Filtration makes water clearer by removing suspended solids, but does NOT make it pure or safe to drink.
- Distillation or reverse osmosis is needed to remove dissolved substances.
Physical Separation Methods
- Filtration — separates solids from liquids using a porous barrier.
- Sieving — separates particles of different sizes using a mesh (e.g. gravel from sand).
- Evaporation — removes a liquid solvent to leave behind the dissolved solid.
- Magnetic separation — uses a magnet to remove magnetic materials (e.g. iron filings from sand).
- Decanting — carefully pouring off a liquid from a settled solid (e.g. muddy water left to settle).
Words to know
filtration
A way to separate parts of a mixture using a barrier that lets some particles through.
e.g. Filtration removes dirt from muddy water.
mixture
Two or more substances combined but not chemically joined.
e.g. Sand and water make a mixture.
solution
A mixture in which one substance is fully dissolved in another.
e.g. Salt dissolved in water is a solution.
solvent
The substance, usually a liquid, that dissolves another substance.
e.g. Water is a common solvent.
impurity
Something extra in water that does not belong, like dirt or germs.
e.g. A filter removes impurities from drinking water.
particle size
How big the bits of a substance are.
e.g. A filter traps particles too large to pass through.
Tip: filtration works because the filter holes are smaller than the solid particles being removed. The liquid and any dissolved substances pass straight through.
Unlock the full HSEA system for 7 days.
Add your first kid profile and your 7 days start: every lesson in every grade, saved progress for each child. Nothing to set up, no card required, nothing to cancel.
- ✓ All 1,880 lessons, Grades 1–6, every subject
- ✓ Profiles + saved progress for every kid
- ✓ Printable lessons with answer key