No single filter removes everything. The right choice depends on what is in your water, how much you need, and whether you have electricity and water pressure. Use this guide to compare technologies, understand certifications, and choose systems for homes, emergencies, and whole communities.
Step 1: Know What’s in Your Water
- City water (U.S.): Read your utility’s annual Consumer Confidence Report, and test for lead if your home was built before 1986.
- Private wells: Test at least once a year for bacteria, nitrates, and pH, and every few years for arsenic, lead, and other local contaminants.
- Outside the U.S. or in the field: Assume surface water is contaminated with pathogens and treat it before drinking.
- Use a state-certified laboratory for reliable results.
Household Filter and Treatment Technologies
| Technology | Removes | Does not remove | Best for |
|---|---|---|---|
| Activated carbon (pitchers, faucet mounts, under-sink, fridge) | Chlorine, taste and odor, many VOCs and pesticides; lead and PFAS if certified | Most bacteria and viruses, dissolved minerals, nitrates, fluoride | Improving treated city water |
| Reverse osmosis (RO) | Dissolved salts, lead, arsenic, fluoride, nitrates, PFAS, most microbes | Some dissolved gases; membrane defects can let microbes pass | Heavy chemical contamination; desalination |
| Ultraviolet (UV) light | Inactivates bacteria, viruses, and protozoa | Chemicals, metals, sediment; needs clear water | Wells and rainwater, paired with a sediment or carbon filter |
| Ceramic filters | Bacteria, protozoa, sediment | Most viruses and chemicals (unless carbon core) | Low-cost household use in developing regions |
| Hollow-fiber membranes (microfiltration, ultrafiltration) | Bacteria and protozoa; ultrafiltration also removes many viruses | Dissolved chemicals and salts | Portable, gravity, and emergency filters |
| Distillation | Minerals, heavy metals, most microbes | Some volatile chemicals that boil with water | Small volumes of very pure water |
| Ion exchange / softeners | Hardness (calcium, magnesium); specialty resins target nitrate or arsenic | Microbes and most organic chemicals | Hard water and scale control |
| Sediment filters | Sand, rust, silt | Microbes and dissolved contaminants | Pre-filtering before carbon, RO, or UV |
| Biosand filters | Most bacteria and protozoa, turbidity, some viruses | Dissolved chemicals and salts | Community and household use without electricity |
| Chlorination | Bacteria and viruses | Cryptosporidium, chemicals, sediment | Disinfecting stored and piped water |
Filter Certifications Explained
Look for independent certification from NSF International, IAPMO, or the Water Quality Association, and check that the product is certified for the specific contaminant you care about, not just “filters water.”
| Standard | What it covers |
|---|---|
| NSF/ANSI 42 | Aesthetic effects: chlorine, taste, odor, particulates |
| NSF/ANSI 53 | Health effects: lead, cysts, VOCs, and PFOA/PFOS, among others |
| NSF/ANSI 58 | Reverse osmosis systems |
| NSF/ANSI 55 | Ultraviolet disinfection systems (Class A for disinfection) |
| NSF/ANSI 62 | Distillation systems |
| NSF/ANSI 44 | Water softeners |
| NSF/ANSI 401 | Emerging contaminants: some pharmaceuticals, pesticides, and more |
| NSF/ANSI 177 | Shower filters (free chlorine reduction) |
| NSF P231 / EPA Guide Standard | Microbiological water purifiers for field and emergency use |
Match the Treatment to the Problem
| If your concern is… | Consider |
|---|---|
| Chlorine taste and odor | Carbon filter (NSF 42) |
| Lead | Carbon filter certified to NSF 53 for lead, or RO (NSF 58) |
| Bacteria and viruses | UV, boiling, chlorination, or a certified purifier |
| Giardia and Cryptosporidium | Filters rated 1 micron absolute or smaller, UV, RO, or boiling |
| Arsenic | RO or specialty adsorption media; test for arsenic type |
| Nitrates | RO or nitrate-selective ion exchange |
| PFAS | RO or carbon certified to NSF 53 or 58 for PFAS |
| Salt water or brackish water | Reverse osmosis desalination |
| Hard water and scale | Water softener or scale-reduction system |
Emergency and Field Treatment
Boiling
Bring water to a rolling boil for 1 minute (3 minutes above 6,500 feet), then let it cool. Boiling kills pathogens but does not remove chemicals.
Household Bleach
Use unscented bleach. For regular bleach at 6%, the CDC recommends about 8 drops (1/8 teaspoon) per gallon of clear water. Stir and wait 30 minutes; the water should have a slight chlorine smell. Filter cloudy water first.
Solar Disinfection (SODIS)
Fill clear plastic PET bottles with low-turbidity water and leave them in full sunlight for at least 6 hours, or 2 days if cloudy. UV and heat inactivate most pathogens. Best where nothing else is available.
Portable Filters
Gravity bags, squeeze filters, and straw filters with hollow-fiber membranes remove bacteria and protozoa. Pair with chemical treatment if viruses are a concern.
Tablets
Chlorine dioxide tablets are effective against bacteria, viruses, and, with longer contact time, Cryptosporidium. Follow the label timing.
Storage
Store at least 1 gallon per person per day for at least 3 days (2 weeks if possible) in clean, food-grade containers, away from sunlight and chemicals.
Community-Scale Water Systems
| System | How it works | Where it fits |
|---|---|---|
| Solar-powered boreholes | Deep wells with solar pumps deliver water to taps and storage tanks | Rural villages with groundwater, such as the wells of Water for West Africa |
| Solar desalination | Solar power runs reverse osmosis that turns seawater or brackish water into drinking water | Coastal communities, like the Ice in a Box system for San Evaristo, Mexico |
| Water kiosks | Centralized treatment (often RO or UV) with jugs sold or distributed locally | Towns and peri-urban neighborhoods |
| Chlorine dispensers | A dispenser at the water point lets users dose each container | Community wells and springs |
| Rainwater catchment | Roofs and tanks collect rain for schools and clinics | Areas with seasonal rainfall |
| Protected springs and gravity-fed systems | Spring boxes and pipes deliver water without pumps | Hilly and mountain regions |
| Atmospheric water generators | Condense water from humid air | Specialized uses; energy-intensive |
| Nature-based solutions | Wetlands, reforestation, and watershed restoration protect source water | Long-term watershed health |
Water-Saving Systems and Fixtures
| System | Typical savings or benefit |
|---|---|
| WaterSense toilets (1.28 gpf or less) | 20% or more less water than the 1.6 gpf standard; far more versus older 3.5 to 7 gpf toilets |
| WaterSense showerheads (2.0 gpm or less) | At least 20% less than standard 2.5 gpm heads |
| Faucet aerators (1.5 gpm or less) | About 30% less than standard 2.2 gpm faucets |
| Smart irrigation controllers | Adjust watering to weather and soil moisture |
| Drip irrigation | Delivers water to roots with little evaporation or runoff |
| Rain barrels and cisterns | Free water for gardens and, with treatment, other uses |
| Greywater systems | Reuse of laundry and shower water for landscapes |
| Hot water recirculation pumps | Stop running the tap while waiting for hot water |
| Leak detectors and smart water meters | Catch hidden leaks early |
Maintenance Matters
- Replace cartridges on schedule; an old carbon filter can release trapped contaminants and grow bacteria.
- Replace UV lamps yearly and clean the quartz sleeve.
- Sanitize RO systems and change pre-filters every 6 to 12 months; membranes every 2 to 5 years.
- Clean ceramic candles gently and replace them if cracked.
- Keep storage tanks covered and clean.
Reference Sources
- NSF: Home water treatment and certified products
- CDC: Making water safe in an emergency
- EPA: Consumer Confidence Reports
- WHO: Guidelines for drinking-water quality
- CAWST: Household water treatment knowledge base
- SODIS: Solar water disinfection
This guide is for general information. For health-related decisions, follow your local health authority and have your water tested by a certified laboratory.