A. O. Smith Reverse Osmosis Systems: 3 Picks Ranked by Specs

Quick picks

Our 3 picks

1 Best overall

A. O. Smith 2-Stage Under Sink Filter

Best for: small households wanting certified contaminant reduction

Filtration Stages

2

Design

Under sink

Certification

NSF/ANSI 42, 43, 401, WQA

Contaminants Removed

Lead, PFAS, chlorine, mercury, asbestos

Installation Type

Under sink

Features

Chlorine Reduction

View on Amazon: A. O. Smith 2-Stage Under Sink Filter Affiliate link

This under sink unit uses a 2-stage Claryum filter to reduce 99% of 78 contaminants, including lead, PFAS, and chlorine. It maintains essential minerals and does not reduce TDS. Certified to NSF/ANSI Standards 42, 43, and 401, it filters at 0.5 gallons per minute. The system fits families of 1 to 4 and requires no plumber for installation.

Pros

• Reduces 99% of 78 harmful contaminants
• Certified to NSF/ANSI Standards 42, 43, and 401
• Filters at 0.5 gallons per minute
• No water waste during filtration

Cons

• Does not reduce total dissolved solids
• Requires filter replacement every 6 months
• Limited to 2-stage filtration

Good fit if

• You want certified contaminant reduction
• You need a simple under sink setup
• You prefer water with essential minerals

Skip if

• You need reverse osmosis purification
• You want to reduce TDS levels
• You need high flow rate for large families

Verdict: A. O. Smith 2-Stage Under Sink Filter offers certified contaminant reduction without TDS removal. It suits small households seeking straightforward under sink purification with mineral retention.

2 Best budget

A. O. Smith Advanced Direct Connect

Best for: Fast-flow mineral retention under-sink filtration

Design

Under sink

Certification

NSF/ANSI 42, 53, 401, IAPMO

Contaminants Removed

Lead, PFAS, chlorine, microplastics

Installation Type

Under sink

Features

Chlorine Reduction

Dimensions

4 × 4 × 20 inches

View on Amazon: A. O. Smith Advanced Direct Connect Affiliate link

The A. O. Smith AO-MF-ADV is an under-sink water filter that connects directly to your cold water line. It uses Advanced Claryum filtration to reduce up to 99% of 78 contaminants, including lead and PFAS, while keeping beneficial minerals. Certified to NSF/ANSI 42, 53, and 401 standards, it delivers a fast 1.5 GPM flow rate. This system fits in tight spaces and requires no additional faucet, making it a practical choice for improving taste and odor without reverse osmosis wastewater.

Pros

• Reduces up to 99% of 78 contaminants including lead and PFAS
• Fast 1.5 gallons per minute flow rate for daily use
• IAPMO certified to NSF/ANSI 42, 53, and 401 standards
• No additional faucet required for installation

Cons

• Does not reduce Total Dissolved Solids (TDS)
• Filter capacity limited to 784 gallons or 6 months
• Limited to 78 contaminants rather than broader reduction

Good fit if

• You want to improve taste and odor without losing minerals
• You need a fast flow rate for a family of four or more
• You prefer a simple under-sink install without extra faucets

Skip if

• You require reverse osmosis to reduce TDS levels
• You need a system with a larger filter capacity
• You want a countertop or faucet-mounted unit instead

Verdict: A. O. Smith AO-MF-ADV Under Sink Filter is a compact, high-flow solution for households prioritizing mineral retention and rapid water delivery over total dissolved solids reduction.

3 Best premium

A. O. Smith 800 GPD Tankless RO

Best for: High-output tankless under-sink filtration

Capacity (GPD)

800 GPD

Design

Tankless, under sink

Certification

NSF/ANSI 42, NSF/ANSI 58, NSF/ANSI 372

Filtration Type

Reverse osmosis

Contaminants Removed

TDS, chlorine, taste, odor

Installation Type

Under sink

View on Amazon: A. O. Smith 800 GPD Tankless RO Affiliate link

This A. O. Smith system delivers 800 GPD of reverse osmosis filtration without a storage tank. Its slim 17.3-inch length fits under most sinks. It holds IAPMO certification to NSF/ANSI 58 and 372 standards. The unit includes built-in leak detection with auto shutoff. You get clean water faster for daily use. It suits those needing high output in tight spaces.

Pros

• 800 GPD tankless capacity for fast flow
• Slim 17.3 x 5.1 x 15.5 inch footprint
• Certified to NSF/ANSI 58 and 372
• Built-in leak detection with audible alarm

Cons

• Heavier at 15.8 pounds than tank models
• 2-year limited warranty is shorter than industry standard
• No mention of smart app connectivity

Good fit if

• You need high daily water output
• You have limited under-sink cabinet space
• You want certified contaminant reduction

Skip if

• You prefer a traditional tank system
• You need remote monitoring via app
• You want a longer warranty period

Verdict: A. O. Smith 800 GPD Tankless RO fits homes with tight under-sink spaces that require high daily water output. It provides certified filtration and smart leak protection for busy households.

Specifications side by side

A. O. Smith Reverse Osmosis Systems: 3 Picks Ranked by Specs

A. O. Smith offers three distinct under-sink models tailored to different household needs. The A. O. Smith 2-Stage Under Sink Filter provides certified contaminant reduction while retaining minerals. This unit measures 11.7 inches in length and weighs 4 pounds, making it suitable for small households seeking straightforward purification without total dissolved solids removal.

For higher output, the A. O. Smith 800 GPD Tankless RO delivers up to 800 gallons per day. Its tankless design saves space under the sink, and it includes smart leak protection. The A. O. Smith Advanced Direct Connect serves as a compact, high-flow alternative that prioritizes mineral retention and rapid water delivery over extensive filtration stages.

Where A. O. Smith fits

A. O. Smith covers three distinct under-sink niches. You can choose a compact 2-stage filter for small households needing certified contaminant reduction. A high-flow mineral retention unit suits those prioritizing rapid delivery. The 800 GPD tankless system fits tight spaces requiring high daily output. Sizes range from 4 inches wide to 17.3 inches long. None of these models include a built-in storage tank. You also will not find a countertop option in this lineup. The brand focuses entirely on under-sink installation for steady, clean water.

How to Choose the Right A. O. Smith System

1. Check Filtration Stages

   You should first decide if you need simple contaminant reduction or full reverse osmosis purification. The A. O. Smith 2-Stage Under Sink Filter offers certified contaminant reduction without removing total dissolved solids. This model suits small households wanting straightforward under-sink purification with mineral retention. If you require deeper purification, you must look at systems with additional stages. The number of stages directly impacts the water quality you receive at the tap. Choose based on your specific purity needs.

2. Consider Tankless Design

   If you have limited under-sink space, a tankless design is essential. The A. O. Smith 800 GPD Tankless RO fits homes with tight under-sink spaces that require high daily water output. It provides certified filtration and smart leak protection for busy households. This brushed nickel unit measures 15.5 inches in height and 17.3 inches in length. You save counter space by eliminating the storage tank. This design is ideal for modern kitchens where storage is at a premium.

3. Evaluate Water Capacity

   Your daily water usage determines the required gallons per day capacity. The A. O. Smith 800 GPD Tankless RO delivers high output for busy families. This capacity ensures you have enough purified water for cooking and drinking without waiting for a tank to refill. Lower capacity systems may struggle during peak usage times. You should match the GPD rating to your household size. Higher capacity provides convenience and reduces wait times for fresh water at the faucet.

4. Assess Physical Dimensions

   You must measure your under-sink cabinet before purchasing any unit. The A. O. Smith Advanced Direct Connect model is compact, measuring 4 inches in width and height. It stands 20 inches tall and weighs 5.1 pounds. This size fits easily into standard cabinets without crowding other items. The 2-stage filter measures 11.7 inches in length. Always verify your available space against these dimensions. Proper sizing ensures easy installation and maintenance access for future filter changes.

5. Review Mineral Retention

   Some users prefer water that retains natural minerals for better taste. The A. O. Smith Advanced Direct Connect filter is a compact, high-flow solution for households prioritizing mineral retention. It delivers rapid water delivery over total dissolved solids reduction. This feature is beneficial if you dislike the flat taste of fully purified water. You get clean water with essential minerals intact. Choose this option if flavor and speed are more important than absolute purity.

Frequently asked questions

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