Water is water, right? Not quite. Where your water comes from — and what it picks up along the way — determines what a filter actually needs to remove. Understanding the basics of the water cycle and the different types of drinking water makes it much easier to choose the right filtration for your home. No chemistry degree required — just the plain facts.
The Hydrologic Cycle
Every drop of drinking water has traveled through the hydrologic cycle: evaporation, condensation, precipitation, and collection. Heat from the sun turns surface water into vapor (evaporation). That vapor cools and condenses into clouds (condensation), then falls back to earth as rain or snow (precipitation). From there, water gathers in rivers and lakes or seeps underground into aquifers (collection and infiltration), where it may sit for days or thousands of years before reaching your tap.
Along the way, water picks up a little bit of everything it touches. Dissolving rock adds natural minerals like calcium and magnesium. Rain and runoff carry sediment and silt. Agricultural runoff can contribute nitrates and pesticides. Industrial activity can leave behind heavy metals and chemical contaminants. And by the time water reaches a municipal treatment plant, chlorine or chloramine is usually added to kill germs — which protects against disease but leaves a taste and odor many people dislike.
That’s why filtration matters: a good filter targets what’s actually in your water — the minerals, sediment, chemicals, and disinfectants — without stripping out everything or adding anything you didn’t ask for.
Types of Drinking Water & Filtration
Spring water
What it is: Water that flows naturally to the surface from an underground aquifer, bottled or piped at the source.
Pros: Contains natural minerals and usually tastes pleasant.
Cons: Quality varies by source; can be affected by runoff and contamination; bottled versions create plastic waste.
Distilled water
What it is: Water boiled into steam and condensed back into liquid, leaving most impurities behind.
Pros: Removes nearly all dissolved solids, minerals, and many contaminants; very consistent purity.
Cons: Flat taste; removes beneficial minerals too; home distillation is slow and energy-hungry.
Reverse osmosis (RO) water
What it is: Water forced through a semipermeable membrane that blocks dissolved solids, lead, fluoride, nitrates, and many chemicals.
Pros: Very thorough contaminant removal; affordable, widely available systems.
Cons: Wastes some water during filtration; strips healthy minerals (often re-added afterward); slower flow rate.
Microfiltration
What it is: Water passed through a filter with pores around 0.1 microns, catching sediment, cysts, and some bacteria.
Pros: Simple, low-pressure, and inexpensive; great as a pre-filter or for clearer-tasting water.
Cons: Doesn’t remove dissolved chemicals, heavy metals, or viruses.
Ultrafiltration
What it is: Membrane filtration with pores around 0.01 microns — fine enough to trap most bacteria and many viruses while letting minerals through.
Pros: Removes pathogens without electricity or high pressure; keeps natural minerals.
Cons: Doesn’t remove dissolved chemicals, salts, or heavy metals.
Nanofiltration
What it is: A membrane step between ultrafiltration and reverse osmosis, targeting small organic molecules and some dissolved salts.
Pros: Softens water and removes many organics with less pressure and waste than RO.
Cons: Less thorough than RO for heavy metals and fluoride; less common in home systems.
Deionized water
What it is: Water stripped of nearly all mineral ions using ion-exchange resins.
Pros: Extremely pure; ideal for labs, aquariums, and appliances like steam irons.
Cons: Aggressively leaches minerals (including from pipes); not meant as everyday drinking water; flat taste.
Alkaline/remineralized water
What it is: Water with a raised pH (usually 8+) or added minerals like calcium and magnesium — often made by RO systems with a remineralization stage.
Pros: Tastes better than plain RO water; adds back some minerals.
Cons: Health claims beyond taste and hydration are unproven; alkaline ionizers can be expensive.
Want to see how these water types connect to real-world filters? Our “What’s In Your Water?” guide is the product guide that matches filtration options to what’s actually in your tap water.