Create a mini water filter

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.

1. Cotton (top layer) — traps the largest particles such as leaves and large debris.
2. Charcoal (second layer) — absorbs chemicals, odors, and very fine particles.
3. Sand (third layer) — traps fine sediment and smaller particles.
4. Gravel (bottom layer) — supports the layers above and removes the largest solid pieces as water first enters.

Pure vs Impure Water

• Pure water contains only H2O molecules — no dissolved minerals, gases, or particles.
• Impure water (tap, river, sea) contains dissolved salts, minerals, gases, or suspended particles.
• Filtration makes water clearer by removing suspended solids, but does NOT make it chemically pure.
• 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).