By SCWS Team
February 1, 2025 · 12 min read
Want the purest drinking water possible from your well? Reverse osmosis removes up to 99% of everything in your water—minerals, heavy metals, nitrates, bacteria, even pesticides. It's the gold standard of home water purification. But RO systems aren't for everyone, and well water presents unique challenges. Here's what you need to know before investing in an RO system.
How Reverse Osmosis Works
Reverse osmosis is a water purification process that uses pressure to force water through a semi-permeable membrane. This membrane has microscopic pores—approximately 0.0001 microns—that allow water molecules to pass through while blocking virtually everything else.
Think of it like a very fine screen: water molecules are small enough to squeeze through, but dissolved minerals, contaminants, bacteria, and other impurities are too large and get rejected. The rejected contaminants are flushed away as wastewater, while pure water collects in a storage tank.
The Multi-Stage Filtration Process
A well water RO filter typically includes multiple filtration stages beyond just the membrane:
- Stage 1 - Sediment pre-filter: Removes sand, silt, rust, and particles down to 5 microns. Essential for well water to protect the membrane.
- Stage 2 - Carbon pre-filter: Absorbs chlorine, chloramines, and organic chemicals. Protects membrane from chemical degradation.
- Stage 3 - RO membrane: The heart of the system. Removes 95-99% of dissolved solids, including minerals, heavy metals, and bacteria.
- Stage 4 - Carbon post-filter: "Polishes" the water, removing any remaining tastes or odors before the water reaches your glass.
- Stage 5 (optional) - Remineralization: Some systems add back beneficial minerals like calcium and magnesium for taste and health benefits.
What Reverse Osmosis Removes From Well Water
RO is the most comprehensive water treatment method available for residential use. Here's what a reverse osmosis well water system removes:
| Contaminant Category | Examples | Removal Rate |
|---|---|---|
| Dissolved Minerals | Calcium, magnesium, iron, manganese | 95-99% |
| Heavy Metals | Lead, arsenic, mercury, chromium | 95-99% |
| Nitrates/Nitrites | Agricultural runoff contaminants | 85-95% |
| Microorganisms | Bacteria, viruses, cysts | 99%+ |
| Chemicals | Pesticides, herbicides, VOCs | 95-99% |
| Total Dissolved Solids | TDS (all dissolved substances) | 95-99% |
| Sodium | From water softeners or natural sources | 95-98% |
For well owners dealing with specific contaminants like iron, bacteria, or hard water, RO provides a comprehensive solution—though pre-treatment is often necessary to protect the membrane.
Under-Sink vs Whole-House RO Systems
One of the biggest decisions when choosing an RO system well owners face is whether to treat just drinking water or the entire home's water supply.
Under-Sink RO Systems
These compact units install under your kitchen sink and include a dedicated faucet for purified water. They're the most popular choice for well owners.
Advantages:
- Affordable: $200-$600 installed
- Treats only drinking/cooking water, minimizing waste
- Easy DIY installation in most cases
- Low maintenance costs ($50-$100/year for filters)
- Produces 50-100 gallons per day—plenty for a family
Limitations:
- Only treats one location
- Doesn't address shower/bath water
- Requires space under sink for tank
Whole-House RO Systems
These large-capacity systems treat all water entering your home, providing purified water at every tap, shower, and appliance.
Advantages:
- Purified water throughout entire home
- Protects all appliances from scale and minerals
- Ideal for severe contamination situations
- No need for multiple treatment systems
Limitations:
- Expensive: $3,000-$5,000+ installed
- Significant water waste (hundreds of gallons daily)
- Requires large storage tank
- Higher maintenance costs
- May require booster pump for adequate pressure
- Removes beneficial minerals from all water
Our recommendation: For most well owners, an under-sink RO system for drinking water combined with targeted whole-house treatment (water softener, sediment filter, or UV sterilization) provides the best balance of effectiveness, cost, and practicality.
💡 Best Value for Most Homeowners
An under-sink RO system ($200-$600) treats your drinking and cooking water at a fraction of the cost of whole-house treatment. Combine with a water softener for hard water issues and you've got comprehensive protection without breaking the bank.
Pre-Treatment Requirements for Well Water
Well water presents unique challenges for RO systems. Unlike municipal water, it hasn't been pre-treated—so your RO system faces raw groundwater conditions that can quickly damage the membrane.
Essential Pre-Treatment
- Sediment filtration: A 5-micron sediment pre-filter is mandatory. Well water contains sand, silt, and particulates that will clog the membrane within weeks without pre-filtration.
- Water softening: If your well water exceeds 7 grains per gallon hardness, install a water softener before the RO system. Hard water scale destroys RO membranes rapidly—reducing their 2-3 year lifespan to under a year.
- Iron/manganese removal: If your water contains more than 0.3 ppm iron or 0.05 ppm manganese, you'll need an iron filter upstream. These minerals foul RO membranes and can't be adequately removed by sediment filtration alone.
Recommended Pre-Treatment
- Carbon pre-filtration: Removes chlorine (if you've added it for disinfection), pesticides, and organic compounds that can degrade the membrane.
- UV sterilization: For wells with bacterial contamination, UV treatment before the RO system provides an extra layer of protection.
Before installing an RO system, get a comprehensive well water test to identify what pre-treatment you'll need. This prevents expensive membrane damage and ensures your system performs optimally.
Waste Water Considerations
RO systems don't just filter water—they flush contaminants away as wastewater. This is both the technology's strength and its main drawback.
Typical Waste Ratios
| System Type | Pure:Waste Ratio | Daily Waste (3 gal/day use) |
|---|---|---|
| Standard RO | 1:3 to 1:4 | 9-12 gallons |
| High-efficiency RO | 1:1 to 2:1 | 1.5-3 gallons |
| Whole-house RO | 1:3 to 1:5 | 300-500+ gallons |
Minimizing Water Waste
- Choose high-efficiency systems: Modern "zero waste" RO units recirculate rejected water, achieving 1:1 or better ratios.
- Capture wastewater: Redirect the waste line to water plants, fill toilets, or use for cleaning. This "gray water" still contains minerals but is perfectly usable.
- Use under-sink only: Limiting RO to drinking water keeps waste manageable—9-12 gallons daily vs. hundreds with whole-house systems.
- Maintain your system: A well-maintained RO system operates more efficiently. Dirty pre-filters reduce pressure and increase waste.
Maintenance Requirements
RO systems require regular maintenance to function properly and protect your investment. Here's what to expect:
Filter Replacement Schedule
- Sediment pre-filter: Every 6-12 months (more frequently with high-sediment well water)
- Carbon pre-filter: Every 6-12 months
- RO membrane: Every 2-3 years with proper pre-treatment; 1 year or less without
- Carbon post-filter: Every 12 months
- Storage tank: Sanitize annually; replace every 5-7 years
Annual Maintenance Costs
- Under-sink systems: $50-$150/year for filters
- Whole-house systems: $200-$500/year for filters and membrane
- Professional maintenance: $100-$200/year if you prefer expert service
Cost Comparison: RO System Options
| System Type | Equipment | Installation | Annual Maintenance |
|---|---|---|---|
| Basic under-sink RO | $150-$300 | $0-$150 (DIY possible) | $50-$75 |
| Premium under-sink RO | $300-$600 | $100-$200 | $75-$150 |
| Tankless under-sink RO | $400-$800 | $100-$200 | $100-$150 |
| Whole-house RO | $2,000-$4,000 | $1,000-$2,000 | $200-$500 |
| Commercial-grade whole-house | $4,000-$8,000+ | $1,500-$3,000 | $400-$800 |
Bottom line: Most well owners spend $200-$500 for an under-sink system that provides years of pure drinking water. Whole-house systems make sense only for severe contamination situations where all water contact needs treatment.
Pros and Cons of RO for Well Water
Advantages
- Removes 95-99% of all contaminants
- Eliminates bacteria, viruses, and parasites
- Removes nitrates, arsenic, lead, and heavy metals
- Significantly improves taste and odor
- Reduces TDS to near-pure levels
- No chemicals required for treatment
- Removes sodium from softened water
- Relatively affordable for under-sink systems
- Low ongoing maintenance requirements
Disadvantages
- Wastes 1-4 gallons per gallon produced
- Removes beneficial minerals (calcium, magnesium)
- Requires pre-treatment for most well water
- Slow production rate (50-100 GPD typical)
- Whole-house systems are expensive
- Regular filter replacement required
- Under-sink units treat only one tap
- Membranes damaged by chlorine, hard water, iron
- Slightly acidic output water (5.5-6.5 pH)
Frequently Asked Questions
Is reverse osmosis good for well water?
Yes, reverse osmosis is excellent for well water treatment. RO systems remove 95-99% of dissolved contaminants including minerals, heavy metals, nitrates, bacteria, and chemicals that are common in well water. However, well water typically requires pre-treatment (sediment filter, water softener) to protect the RO membrane from damage. For most well owners, an under-sink RO system for drinking water combined with whole-house pre-filtration provides the best results.
How much does an RO system for well water cost?
RO system costs vary widely based on type and capacity. Under-sink RO systems cost $200-$600 for the unit plus $100-$200 for installation. Whole-house RO systems range from $3,000-$5,000+ including installation. Annual maintenance costs $50-$150 for filter replacements. Most well owners find under-sink systems provide the best value, treating drinking and cooking water while avoiding the high costs and water waste of whole-house RO.
What does reverse osmosis remove from well water?
Reverse osmosis removes virtually everything from well water except pure H2O. This includes: dissolved minerals (calcium, magnesium, iron), heavy metals (lead, arsenic, mercury), nitrates and nitrites, bacteria and viruses, pesticides and herbicides, fluoride and chlorine, total dissolved solids (TDS), and sodium. RO typically achieves 95-99% removal rates, producing water with TDS below 50 ppm from well water that may have started at 500+ ppm.
How much water does an RO system waste?
Traditional RO systems produce 3-4 gallons of wastewater for every 1 gallon of purified water (25% efficiency). High-efficiency models achieve 1:1 or even 2:1 pure-to-waste ratios. For an under-sink system producing 3 gallons of drinking water daily, expect 9-12 gallons of wastewater with standard units or 3-6 gallons with high-efficiency models. This wastewater can be captured for plants, cleaning, or other non-drinking uses to minimize waste.
Do I need a water softener before my RO system?
If your well water is hard (above 7 grains per gallon), yes—a water softener before your RO system is strongly recommended. Hard water causes calcium and mineral scale to build up on the RO membrane, dramatically reducing its lifespan from 2-3 years to just 6-12 months. The softener removes hardness minerals before they reach the membrane. At minimum, use a sediment pre-filter and consider a water softener or scale inhibitor for water above 10 gpg hardness.
Need Help Choosing a Water Treatment System?
Whether you're considering reverse osmosis, a water softener, or a comprehensive treatment system for your well, we can help you evaluate your options. Start with professional water testing to understand exactly what contaminants you're dealing with—then choose the right treatment approach for your specific situation.