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Finding the best reverse osmosis systems with 1 1 pure to drain helps you reduce water waste without sacrificing output. The Waterdrop G2 400 GPD Tankless RO leads this list because its tankless design saves space while maintaining that efficient ratio. We compared 7 models using only the specifications published on their listings. Each pick focuses on a specific need, from alkaline remineralization to UV sterilization. This guide helps you decide which filtration stage and flow rate match your kitchen setup and water source.
01 Check filtration stages and capacity
You should compare filtration stages and capacity before buying. Most models offer six or seven stages. The Waterdrop G2 provides 400 GPD output. The iSpring PH100 delivers 100 GPD. Higher capacity means faster water flow. More stages remove additional contaminants. Match these specs to your daily water needs and sink space.
| # | Product | Best for | Price |
|---|---|---|---|
| 1 | Waterdrop G2 400 GPD Tankless RO Best overall | space-saving, water-efficient filtration | |
| 2 | iSpring PH100 100 GPD Alkaline RO Best budget | Water conservation and improved taste | |
| 3 | Home Master Artesian Full Contact Also great | mineral-rich water with high water efficiency | |
| 4 | Home Master TMHP 9-Stage RO Best premium | homes wanting mineral-rich, germ-free water | |
| 5 | Home Master TMULTRA-ERP-L RO System Also great | well water users needing UV sterilization | |
| 6 | Home Master TMULTRA-ERP RO System Also great | well water with iron and UV needs | |
| 7 | Home Master TM-ERP-L Undersink RO Also great | Efficient water use and chloramine removal |
02 The best fit for you
- You want the most compact tankless model – Waterdrop G2 400 GPD Tankless RO – The Waterdrop G2 measures 5.9 inches wide and uses a tankless design.
- You need UV sterilization for well water – Home Master TMULTRA-ERP-L RO System – The Home Master TMULTRA-ERP-L includes a UV filter for well water safety.
- You want a 9-stage system with minerals – Home Master TMHP 9-Stage RO – The Home Master TMHP offers 9 filtration stages including UV and remineralization.
03 Is a 1:1 Pure to Drain Ratio Worth the Upgrade?
A 1:1 pure to drain ratio means for every gallon of filtered water you get, only one gallon goes down the drain. This halves the waste compared to older 3:1 systems. You see this efficiency in models like the Waterdrop G2 and iSpring PH100. It matters if you live in an area with water restrictions or want to lower your household water usage. The technology often involves permeate pumps, like those in the Home Master units, to recover water that would otherwise be wasted.
Worth it if
- You want to reduce daily water waste
- You live in a region with strict water conservation rules
- You prioritize efficiency over maximum flow speed
Skip it if
- You need high-volume output for large families
- You prefer tankless systems without added pump complexity
- You have ample water supply and do not mind higher waste
Waterdrop G2 400 GPD Tankless RO
Best for: space-saving, water-efficient filtration
- Pure to Drain Ratio
- 1:1 Pure to Drain
- Installation Type
- Under-sink
- Daily Production Rate
- 400 GPD
- Filtration Stages
- 7-stage
- Certifications
- NSF/ANSI 372
- Features
- Tankless
The Waterdrop G2 is a 7-stage, tankless reverse osmosis system with a 400 GPD flow rate. It holds a 1:1 pure-to-drain ratio, which reduces water waste significantly compared to standard models. The unit measures 5.9 by 14 by 17.3 inches and weighs 25 pounds. It requires an under-sink electrical outlet for operation. This system suits you if you need a compact, efficient filtration solution that does not require a storage tank.
- 1:1 pure-to-drain ratio saves water
- 400 GPD flow rate fills a cup in about 12 seconds
- Tankless design saves over 70% of under-sink space
- NSF/ANSI 372 certified for lead-free materials
- Filters replace in 3 seconds with a twist-and-pull design
- 400 GPD daily production rate is lower than the 600 GPD option available
- 25-pound weight is heavier than some comparable undersink systems
- Requires an electrical outlet and drilled holes for installation
- You want a tankless system to maximize under-sink storage space
- You need a 1:1 pure-to-drain ratio to minimize water waste
- You have an electrical outlet available under your sink
- You prefer a system with a higher 600 GPD production rate
- You do not have access to an under-sink electrical outlet
- You want a system that does not require drilling holes for installation
Verdict: The Waterdrop G2 400 GPD Tankless RO is a practical choice for buyers who prioritize water efficiency and space savings over higher daily output. It fits well in kitchens where electrical access is available and storage space is limited.
iSpring PH100 100 GPD Alkaline RO
Best for: Water conservation and improved taste
- Pure to Drain Ratio
- 1:1 Pure to Drain
- Installation Type
- Under-sink
- Daily Production Rate
- 100 GPD
- Filtration Stages
- 6-stage
- Remineralization
- Alkaline remineralization
- Use
- Drinking Water
The iSpring PH100 is a 6-stage under-sink reverse osmosis system with a 100 GPD production rate. It achieves a 1:1 pure to drain ratio, reducing water waste compared to older models. An alkaline remineralization filter restores minerals for better taste. It fits under standard sinks and includes a brushed nickel faucet. This unit suits households prioritizing efficient water use and improved flavor over high volume.
- 1:1 pure to drain ratio for less wasted water
- 100 GPD daily production rate
- 6-stage filtration with alkaline remineralization
- Includes brushed nickel all-metal faucet
- 100 GPD output is slower than the 400 GPD and 75 GPD options on this list
- 16 x 17.5 x 19 inch footprint requires standard under-sink space
- You want a 1:1 pure to drain ratio to conserve water
- You prefer alkaline water with restored minerals for better taste
- You need a standard under-sink system with a metal faucet
- You need high-volume water for large families or ice makers
- You prefer a tankless system for instant flow
- You want a faster fill rate than 100 GPD provides
Verdict: The iSpring PH100 Alkaline RO System offers efficient 1:1 water usage and improved taste through remineralization. It is a solid choice for users who value water conservation and flavor over high-speed output.
Home Master Artesian Full Contact
Best for: mineral-rich water with high water efficiency
- Pure to Drain Ratio
- 1:1 Pure to Drain
- Filtration Stages
- 7-Stages
- Certifications
- NSF Certified
- Remineralization
- 2-Pass Alkaline Remineralization
- Intended Use
- Home
- Dimensions
- 20 × 16 × 12 inches
This Home Master Artesian system uses a 7-stage filtration process with a patented 2-pass alkaline remineralization feature. It includes a non-electric permeate pump to achieve a 1:1 pure to drain ratio, reducing water waste significantly. The unit features catalytic carbon for advanced chemical removal and offers a rapid 4.5-second fill rate for an 8oz glass. It is designed for undersink installation and meets NSF standards for safety and performance.
- 1:1 pure to drain ratio via non-electric permeate pump
- Patented 2-pass alkaline remineralization adds calcium and magnesium
- Catalytic carbon removes chloramines and chlorine effectively
- 4.5-second fill rate for an 8oz glass
- NSF certified components ensure safety and purity
- Includes a storage tank, which adds bulk compared to tankless models
- Weighs 14.5 pounds, making it heavier than some alternatives
- Requires 16x12x20 inches of space under the sink
- You want mineral-rich water with a 1:1 efficiency ratio
- You need a tank-based system for consistent pressure
- You prefer a system with catalytic carbon filtration
- You require a tankless design for maximum space savings
- You have less than 16x12x20 inches of under-sink space
- You want a system without a storage tank
Verdict: Home Master Artesian Alkaline RO delivers efficient water use and enhanced mineral content through its 2-pass remineralization and permeate pump. It suits households that value tank-based reliability and specific filtration stages over compact tankless designs.
Home Master TMHP 9-Stage RO
Best for: homes wanting mineral-rich, germ-free water
- Pure to Drain Ratio
- 1:1 Pure to Drain
- Filtration Stages
- 9-stages
- Remineralization
- 2-pass Alkaline Remineralization
- UV Purification
- UV Sterilizer
- Features
- Alkaline, UV Filter, Remineralization
- Target Contaminant
- Iron
The Home Master TMHP is a 9-stage reverse osmosis system designed for undersink installation. It features a 1:1 pure to drain ratio, which reduces water waste compared to older models. The system includes a UV sterilizer to kill germs and a 2-pass alkaline remineralization stage to improve taste. It measures 15 by 16 by 5 inches. This unit suits households wanting purified water with added minerals and enhanced safety.
- 9-stage filtration removes up to 99% of contaminants
- 1:1 pure to drain ratio saves water
- UV sterilizer kills harmful germs
- 2-pass alkaline remineralization adds healthy minerals
- Non-electric pump reduces water waste
- UV purification requires bulb replacement
- 9-stage process adds complexity compared to 4-stage systems
- You want purified water with added minerals
- You need germ protection via UV sterilization
- You want to minimize water waste with a 1:1 ratio
- You prefer a simpler 4-stage system
- You need a tankless design for space savings
- You want a system with fewer filtration stages
Verdict: Home Master TMHP 9-Stage Alkaline RO delivers clean, mineral-rich water with a water-efficient 1:1 ratio. It fits homes that value germ protection and taste improvement over simple filtration.
Home Master TMULTRA-ERP-L RO System
Best for: well water users needing UV sterilization
- Pure to Drain Ratio
- 1:1 Pure to Drain
- Daily Production Rate
- 75 GPD
- Filtration Stages
- 6-stages
- UV Purification
- UV Sterilizer
- Features
- UV Filter
- Use
- Well Water
This Home Master system handles both city and well water with six filtration stages and a UV sterilizer. It produces 75 gallons per day with a 1:1 pure to drain ratio, thanks to a built-in non-electric permeate pump. The unit measures 16 by 12 by 20 inches and weighs 18 pounds. It includes a brushed nickel faucet and fridge connection kit for convenient installation.
- UV sterilizer kills bacteria and viruses
- 1:1 pure to drain water ratio
- Handles city and well water sources
- Includes brushed nickel faucet and fridge kit
- 75 GPD production rate is lower than 400 GPD models
- 6-stage filtration has fewer stages than 9-stage systems
- 18-pound weight is heavier than tankless units
- You need UV sterilization for well water safety
- You want a 1:1 pure to drain ratio
- You require a faucet and fridge connection included
- You need a flow rate above 75 GPD
- You prefer a tankless design without a storage tank
- You want a system with more than six stages
Verdict: Home Master TMULTRA-ERP-L RO System is a solid choice for homes needing UV protection and efficient water use. It suits buyers who prioritize safety and waste reduction over high-speed flow.
Home Master TMULTRA-ERP RO System
Best for: well water with iron and UV needs
- Pure to Drain Ratio
- 1:1 Pure to Drain
- Filtration Stages
- 6-stage
- UV Purification
- UV Sterilizer
- Features
- UV Filter
- Use
- Well Water
- Target Contaminant
- Iron
The Home Master TMULTRA-ERP is a 6-stage reverse osmosis system designed for both city and well water sources. It features a built-in UV sterilizer to kill bacteria and viruses. The system achieves a 1:1 pure to drain ratio using a non-electric permeate pump. This design reduces water waste and limits TDS creep. It includes an iron prefilter to protect the membrane. The unit measures 16 by 20 inches and weighs 17.4 pounds.
- UV sterilizer kills bacteria and viruses
- 1:1 pure to drain ratio
- Iron prefilter reduces fouling
- Suitable for well and city water
- NSF certified components
- Heavier build at 17.4 pounds
- Fewer filtration stages than competitors
- Larger footprint at 16 by 20 inches
- You need UV sterilization for well water
- You want to minimize wastewater
- You have iron in your water supply
- You prefer tankless designs
- You want more than 6 filtration stages
- You need a smaller footprint
Verdict: Home Master TMULTRA-ERP RO System offers robust protection for well water users who prioritize UV sterilization and water efficiency. It suits those who need iron filtration and can accommodate its larger size and weight.
Home Master TM-ERP-L Undersink RO
Best for: Efficient water use and chloramine removal
- Pure to Drain Ratio
- 1:1 Pure to Drain
- Installation Type
- Undersink
- Daily Production Rate
- 75 GPD
- Certifications
- NSF Certified Components
- Intended Use
- Home
- Dimensions
- 15 × 5 × 16 inches
The Home Master TM-ERP-L is an undersink reverse osmosis system designed for steady water production. It features a 75 GPD membrane and achieves a 1:1 pure to drain ratio using a non-electric permeate pump. The unit includes a 4.5-second fill rate kit and catalytic carbon filtration. This model suits households prioritizing efficient water usage and straightforward maintenance without electricity.
- 1:1 pure to drain waste ratio
- 75 GPD production rate
- Non-electric permeate pump
- Catalytic carbon pre-filter
- 4.5-second faucet fill rate
- 75 GPD output is lower than the 400 GPD and 7 GPD (high flow) options on this list
- 16.8-pound weight and 15x16x5-inch footprint require more under-sink space than tankless models
- Standard 75 GPD membrane produces less daily water than higher-capacity alternatives
- You need a reliable 1:1 waste ratio without electrical connections
- You prefer a traditional tank-based system for consistent pressure
- You want catalytic carbon for chloramine removal
- You require a tankless design to save under-sink space
- You need a flow rate exceeding 75 gallons per day
- You want a system with a digital display or smart connectivity
Verdict: Home Master TM-ERP-L Undersink RO delivers efficient water use with its 1:1 ratio and catalytic carbon filtration. It fits you if you value steady pressure and easy maintenance over maximum speed or compact tankless design.
04 Specifications side by side
| Spec | Waterdrop G2 400 GPD Tankless RO | iSpring PH100 100 GPD Alkaline RO | Home Master Artesian Full Contact | Home Master TMHP 9-Stage RO | Home Master TMULTRA-ERP-L RO System | Home Master TMULTRA-ERP RO System | Home Master TM-ERP-L Undersink RO |
|---|---|---|---|---|---|---|---|
| Installation Type | Under-sink | Under-sink | – | – | – | – | Undersink |
| Daily Production Rate | 400 GPD | 100 GPD | – | – | 75 GPD | – | 75 GPD |
| Filtration Stages | 7-stage | 6-stage | 7-Stages | 9-stages | 6-stages | 6-stage | – |
| Pure to Drain Ratio | 1:1 | 1:1 | 1:1 | 1:1 | 1:1 | 1:1 | 1:1 |
| Certifications | NSF/ANSI 372 | – | NSF Certified | – | – | – | NSF Certified Components |
| Remineralization | – | Alkaline remineralization | 2-Pass Alkaline Remineralization | 2-pass Alkaline Remineralization | – | – | – |
| UV Purification | – | – | – | UV Sterilizer | UV Sterilizer | UV Sterilizer | – |
| Capacity | – | 100 GPD | – | – | – | – | – |
| Features | Tankless | Alkaline, Remineralization | Alkaline, Remineralization | Alkaline, UV Filter, Remineralization | UV Filter | UV Filter | – |
| Use | – | Drinking Water | – | – | Well Water | Well Water | – |
| Target Contaminant | – | – | – | Iron | – | Iron | – |
| Water Source | – | – | – | – | City Water | City Water | – |
| Intended Use | – | – | Home | Home | Home | Home | Home |
| Dimensions | 17.3 × 5.9 × 14 inches | 17.5 × 16 × 19 inches | 20 × 16 × 12 inches | 5 × 15 × 16 inches | 20 × 16 × 12 inches | 20 × 16 × 12 inches | 15 × 5 × 16 inches |
| Weight | 25 pounds | – | 14.5 pounds | – | 18 pounds | 17.4 pounds | 16.8 pounds |
| Size | 400 GPD | – | TMAFC-ERP Permeate Pump | TMHP | TMULTRA-ERP-L Loaded | TMULTRA-ERP w/ Pump | TM-ERP-L Loaded |
| Color | White | White | TMAFC-ERP Permeate Pump | TMHP | White | White | TM-ERP-L Loaded |
| Model | WD-G2-W | PH100 | TMAFC-ERP | TMHP | TMULTRA-ERP-L | TMULTRA-ERP | TM-ERP-L |
If you prefer less wastewater, evaluate the best reverse osmosis systems with 3 1 pure to drain instead.
05 How we picked these systems
We identified systems with a 1:1 pure to drain ratio by scanning Amazon listings for this specific efficiency metric. Only products explicitly stating this ratio in their title or feature list were considered. This ensures you get units that waste less water during the filtration process. We focused strictly on published specifications to maintain accuracy and avoid subjective claims.
The seven systems are ordered by availability first. We then applied a ranking based on the listing's overall rating weighted by the number of ratings. Finally, we sorted by how many guide criteria the specs meet. All details come from the manufacturer data. We do not handle or test these products physically. Prices and stock levels are shown live on the page.
06 How to Choose the Right 1:1 RO System
Check Installation Space
Measure your under-sink area before buying. The Waterdrop G2 is only 5.9 inches wide, making it ideal for tight cabinets. Other models, like the Home Master TMHP, are wider or deeper. Ensure you have enough room for the unit and filter replacements. If space is limited, a tankless design like the Waterdrop G2 saves room. Always verify width, height, and length dimensions against your available space. This prevents installation issues later.
Compare Filtration Stages
Look at the number of filtration stages to ensure thorough contaminant removal. The Home Master TMHP offers nine stages, providing more layers of protection than standard six-stage units. The iSpring PH100 uses six stages with alkaline remineralization. More stages often mean better taste and safety. Choose a system with enough stages for your water quality. Check if the system includes pre-filters and post-filters. This ensures comprehensive coverage for your specific needs.
Assess Daily Capacity
Review the gallons per day (GPD) rating to match your household usage. The Waterdrop G2 provides 400 GPD, suitable for larger families. The iSpring PH100 offers 100 GPD, which may suffice for smaller households. Higher capacity means faster refill rates for your storage tank or direct flow. Consider how much filtered water you use daily. Select a GPD rating that meets your peak demand. This avoids waiting for the system to produce enough water.
Evaluate Water Source
Identify your water source to select the right features. The Home Master TMULTRA-ERP-L includes a UV filter, which is essential for well water safety. It also targets iron contamination. If you use city water, a standard system may suffice. Check the intended use specifications. Well water often requires additional sterilization steps. Ensure the system addresses your specific source challenges. This protects your family from source-specific contaminants effectively.
Review Remineralization
Consider systems with alkaline or remineralization features for better taste. The iSpring PH100 adds minerals back into the water. The Home Master Artesian uses a two-pass remineralization process. These features improve pH levels and flavor. If you prefer neutral-tasting water, skip this feature. Check the feature list for alkaline or remineralization tags. This enhances the drinking experience. It also adds beneficial minerals back after the RO process removes them.
07 Frequently asked questions
How does the Waterdrop G2 save space under my sink?
The Waterdrop G2 400 GPD Tankless RO uses a tankless design to save space. It measures 5.9 inches wide, 14 inches high, and 17.3 inches long. This compact footprint fits well in kitchens where storage space is limited. You do not need extra room for a storage tank.
Which 1:1 RO system is best for well water?
The Home Master TMULTRA-ERP-L is a solid choice for well water users. It includes a UV filter for safety and targets iron contaminants. It also offers a 1:1 pure to drain ratio to reduce waste. This system suits buyers who prioritize safety and efficient water use.
Does the iSpring PH100 improve the taste of my water?
Yes, the iSpring PH100 Alkaline RO System improves taste through remineralization. It is a 6-stage system that adds minerals back into the water. It also maintains a 1:1 pure to drain ratio for water conservation. This makes it a practical choice for users who value flavor.
What is the difference between the Home Master TMHP and TMULTRA-ERP?
The Home Master TMHP is a 9-stage system with UV filtration and remineralization. It targets iron and is designed for general home use. The TMULTRA-ERP is a 6-stage system that also includes a UV filter and targets iron. Both offer a 1:1 pure to drain ratio.
How many filtration stages do these 1:1 RO systems have?
Most models in this list offer six or seven stages. The Waterdrop G2 has seven stages. The iSpring PH100 has six stages. The Home Master TMHP has nine stages, while the TMULTRA-ERP has six. More stages generally remove additional contaminants from your water supply.
Is the Home Master Artesian system tankless or tank-based?
The Home Master Artesian Alkaline RO is a tank-based system. It uses a permeate pump to achieve its 1:1 pure to drain ratio. It offers two-pass remineralization for enhanced mineral content. This design suits households that value reliability and specific filtration stages over compact tankless designs.
Can the Home Master TM-ERP-L remove chloramines?
Yes, the Home Master TM-ERP-L Undersink RO removes chloramines. It uses catalytic carbon filtration for this purpose. The system also delivers efficient water use with its 1:1 ratio. It fits you if you value steady pressure and easy maintenance over maximum speed.
