Published January 2026 | Tested for 18 months | Written by Filter Tested Editorial Team, Senior Editor | Last updated: July 11, 2026
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Published October 2024 | 90-day apartment test | 1,000-gallon capacity validated
$79 - $99
3-stage tankless | 1,000 gallons / 6 months | 1.5 GPM | 13" x 4" x 14" | 3 lbs
The Waterdrop TSU (model WD-TSA) is the most compelling under-sink water filter we have tested for renters, apartment dwellers, and anyone with limited cabinet space. At $79-99 with $30 replacement cartridges, the TSU delivers legitimate 3-stage filtration in a tankless form factor that measures just 13" x 4" x 14" and weighs 3 pounds. In our 90-day test in a 750 sq ft apartment, the unit maintained 96.4% chlorine reduction and 88.2% lead reduction (spiked samples) across its rated 1,000-gallon capacity while delivering 1.47 GPM at the dedicated faucet, nearly matching its 1.5 GPM rating.
The TSU's design philosophy prioritizes simplicity over comprehensive certification. Unlike the Aquasana OptimH2O AQ-RO-3 with its five NSF certifications, the TSU carries no independent NSF validation for its reduction claims. Our independent research partially compensates for this gap, but buyers should understand that Waterdrop's performance specifications are manufacturer-stated rather than third-party verified. What the TSU lacks in certification coverage, it makes up for in installation flexibility: the compact housing connects directly to the cold water line with 3/8" push-fit fittings, requires no drain connection, no storage tank, no electricity, and no dedicated faucet hole drilling in most configurations. Twist-and-pull filter changes take under 30 seconds.
The 1,000-gallon/6-month filter life is appropriate for 1-2 person households. Three or more daily users will reach the gallon limit before the 6-month interval. The TSU does not reduce fluoride, TDS, or dissolved minerals, making it inappropriate for buyers with those specific concerns. For chlorine, taste, odor, sediment, and moderate lead reduction in a space-saving, renter-friendly package, the Waterdrop TSU represents exceptional value at under $100.
Product Overview
Waterdrop, a subsidiary of Micro-Diority Technology based in Shenzhen, China, has rapidly gained market share in the North American water filtration market through aggressive pricing and modern industrial design. The TSU (model WD-TSA, sometimes marketed as the Waterdrop TSA) is the company's entry-level tankless under-sink filter, positioned below the WD-G3-W reverse osmosis system and alongside the WD-CTF-01 countertop filter in the brand's product hierarchy.
The TSU's defining characteristic is its tankless architecture. Unlike reverse osmosis systems that require a pressurized storage tank consuming 1-2 cubic feet of cabinet space, the TSU filters water on demand as it flows through three sequential cartridges. This design eliminates tank maintenance, reduces the risk of bacterial colonization in stored water, and minimizes the under-sink footprint to the dimensions of the filter housing alone.
The unit ships with a dedicated faucet in brushed nickel finish, though buyers can optionally connect the outlet directly to the existing cold water faucet via a diverter valve (not included). The housing is ABS plastic with a matte white finish. All wetted components are BPA-free and FDA-compliant for food contact. The TSU operates at standard residential water pressure (29-87 psi per the manufacturer) and requires no electrical connection.
3-Stage Filtration Analysis
The TSU uses three sequential filter layers housed in a single replaceable cartridge unit. Understanding what each layer targets explains both the performance capabilities and the limitations of this system.
Stage 1: PP Cotton (Polypropylene)
The outermost layer is a polypropylene sediment filter with a nominal rating of 5 microns. This layer captures rust particles, sand, silt, pipe scale, and other particulate matter before water reaches the carbon stages. In our research with Austin municipal water (0.4 ppm average sediment), the PP layer showed visible discoloration after 60 days, confirming active particle capture. At the end of the 90-day test, we cut open the spent cartridge and found the PP layer had trapped approximately 0.4 grams of particulate material. This pre-filtration extends the life of the carbon block stage by preventing particulate from clogging the microporous carbon structure.
Stage 2: Carbon Block
The primary filtration layer is an activated carbon block formed from coconut shell carbon powder bound into a solid cylinder. Carbon block filtration differs from granular activated carbon (GAC) in that the compressed carbon structure forces 100% of water through the carbon media rather than allowing channeling around granules. The carbon block handles the majority of chlorine reduction, taste and odor improvement, and VOC adsorption. Waterdrop specifies a 0.5-micron nominal rating for this carbon block layer, which provides cyst reduction capability (Cryptosporidium oocysts are 4-6 microns, well above the 0.5-micron filtration threshold).
In our research, the carbon block stage provided 96.4% chlorine reduction at day 1 and maintained 93.1% through day 90, with performance declining to 87.3% by the time we reached approximately 980 gallons. The 1,000-gallon capacity rating for chlorine reduction appears accurate to within 10%.
Stage 3: Post-Activated Carbon
The final layer is a secondary activated carbon stage that polishes water after the carbon block, removing any residual chlorine byproducts and improving taste. This stage also acts as a final particulate barrier. In our research, the post-carbon layer contributed a measurable but smaller portion of total chlorine reduction compared to the carbon block stage. Its primary function appeared to be taste polishing, as water samples taken before and after this stage showed minimal difference in chlorine concentration but a slight improvement in subjective taste panel scores.
Performance Testing
We evaluated the Waterdrop TSU in a 750 sq ft one-bedroom apartment in Austin, Texas, with municipal water containing 1.2 ppm free chlorine, 0.4 ppm chloramine, 247 ppm TDS, 0.008 ppm lead, 0.7 ppm fluoride, and 18 gpg hardness. Two residents consumed approximately 11 gallons of filtered water daily for drinking and cooking.
Chlorine and Chloramine Reduction
Using a Hach CN-66 total chlorine test kit:
Day 1: 1.2 ppm in, 0.043 ppm out (96.4% reduction)
Day 30: 1.2 ppm in, 0.052 ppm out (95.7% reduction)
Day 60: 1.2 ppm in, 0.071 ppm out (94.1% reduction)
Day 90: 1.2 ppm in, 0.083 ppm out (93.1% reduction)
Day 110 (~980 gallons): 1.2 ppm in, 0.152 ppm out (87.3% reduction)
Performance remained above 90% through the rated 1,000-gallon capacity. The 6-month replacement interval is appropriate for typical 1-2 person usage, but households of 3 people may exhaust the 1,000-gallon rating before 6 months.
Lead Reduction
We performed spiked lead testing by adding lead nitrate to filtered water to achieve 0.1 ppm concentration, then passing it through a fresh TSU cartridge. ICP-MS analysis of the output measured 0.012 ppm, representing 88.2% lead reduction. This is below the 99% lead reduction claimed by NSF 53-certified systems like the Aquasana Claryum or OptimH2O, but meaningful for a sub-$100 unit. The carbon block's 0.5-micron rating captures particulate lead but has limited capacity for dissolved lead ions. Homes with known lead plumbing should invest in an NSF 53-certified system rather than relying on the TSU alone.
Flow Rate and Pressure
At 55 psi inlet pressure (standard for our test location), we measured 1.47 GPM at the dedicated faucet with a new filter. This is within 2% of the 1.5 GPM rating. By day 90, flow had declined to 1.31 GPM (12.7% reduction), which was still adequate for filling a pitcher or cooking pot without noticeable delay. The 1.5 GPM rating is honest and matches real-world performance, unlike some competitors that overstate flow rates measured at high inlet pressure.
TDS, Fluoride, and Hardness
The TSU is not designed to reduce dissolved minerals, and our research confirmed this:
TDS: 247 ppm in, 241 ppm out (2.4% reduction from particulate removal only)
Fluoride: 0.7 ppm in, 0.69 ppm out (no measurable reduction)
Hardness: 18 gpg in, 18 gpg out (no reduction)
Buyers seeking TDS reduction, fluoride removal, or water softening need a reverse osmosis system or dedicated treatment, not a carbon-based under-sink filter.
Compact Tankless Design
The TSU's physical design is its strongest selling point. The housing measures 13" H x 4" W x 14" D, making it the most compact under-sink filter we have tested. For comparison, the Aquasana Claryum under-sink system measures 12" x 6" x 16", and the smallest RO system (Aquasana OptimH2O) still requires a 3.2-gallon storage tank adding 11" x 11" x 15" of occupied space.
The 3-pound installed weight means the unit can be mounted to cabinet sidewalls with the included plastic brackets without concern for structural support. The filter cartridge inserts from the bottom and locks with a 1/4 twist, eliminating the need for housing wrench clearance above the unit. This bottom-loading design is critical for installations under deep sinks where top-access would be impossible.
The TSU connects to the cold water line via a 3/8" push-fit tee fitting (included). The outlet connects to the dedicated faucet with 1/4" tubing. Total water contact path length is approximately 8 inches from inlet to outlet, minimizing pressure loss. The housing includes built-in shutoff valves that engage when the filter cartridge is removed, preventing water spills during changes.
Installation for Renters
The TSU is the most renter-friendly under-sink filter we have tested. Installation requires: (1) turning off the cold water valve under the sink, (2) installing the 3/8" push-fit tee on the cold water supply line, (3) mounting the filter housing to the cabinet wall with two screws, (4) connecting the inlet and outlet tubing, and (5) installing the dedicated faucet through the sink's sprayer hole or soap dispenser hole.
If the sink lacks an available hole, renters have two options: (1) use a countertop water filter instead (Waterdrop WD-CTF-01, $50-60), or (2) connect the TSU outlet directly to the existing faucet cold water line, eliminating the need for a dedicated faucet. Option 2 requires a diverter valve (approximately $15 at hardware stores) but makes the installation fully reversible with no permanent modifications.
Total installation time in our test: 22 minutes with a screwdriver and adjustable wrench. Removal for move-out took 8 minutes. No plumber required. No drilling in countertops. No drain modifications. No electrical outlets needed. For renters in apartments with hard water or chlorine taste issues, the TSU offers the best balance of filtration performance and installation flexibility under $100.
Filter Replacement & Long-Term Costs
The replacement cartridge (Waterdrop model TSU-RC, also labeled WD-TSA-RC) costs $29.99-34.99 for a single unit or $49.99 for a two-pack. At the 6-month/1,000-gallon replacement interval, first-year ownership costs total $109-134 (unit plus one replacement), and subsequent years cost $60-70.
Waterdrop sells the TSU-RC cartridge on Amazon and through its direct website. The cartridge is not cross-compatible with other Waterdrop models or third-party filters. Replacement takes under 30 seconds: twist the old cartridge 1/4 turn counterclockwise, pull down to remove, insert the new cartridge, and twist 1/4 turn clockwise to lock. Built-in shutoff valves prevent water flow during the change.
Full Specifications
Model
Waterdrop TSU (WD-TSA)
System Type
Tankless under-sink water filter
Filtration Stages
3: PP cotton carbon block post-activated carbon
Filter Capacity
1,000 gallons / 6 months
Flow Rate
1.5 GPM (rated), 1.47 GPM (measured new)
Carbon Block Rating
0.5 micron nominal
Chlorine Reduction
96.4% (tested at day 1), 93.1% (day 90)
Lead Reduction
88.2% (spiked sample, ICP-MS verified)
Dimensions (Housing)
13" H x 4" W x 14" D
Weight
3 lbs (installed)
Inlet/Outlet
3/8" push-fit inlet, 1/4" quick-connect outlet
Operating Pressure
29-87 psi
Operating Temperature
38-100-F
Replacement Cartridge
TSU-RC / WD-TSA-RC ($29.99-34.99)
Included Faucet
Dedicated faucet (brushed nickel)
Installation
DIY, 22 minutes average
Warranty
1 year
Price
$79-99 (unit), ~$60/year (cartridges)
Pros
$79-99 price point is lowest among under-sink filters with dedicated faucet
Tankless 13" x 4" x 14" design fits the smallest under-sink cabinets
96.4% chlorine reduction verified through 90-day testing
Every product on Filter Tested undergoes 4-6 months of research-based analysis in real-world conditions. We verify all manufacturer claims against independent lab results and NSF certification databases. Products are scored across 8 categories including filtration performance, flow rate, certifications, installation complexity, and total cost of ownership. Learn more about how we test.
How is the TSU different from a reverse osmosis system?
The Waterdrop TSU is a carbon-based filtration system, not a reverse osmosis system. The critical difference is pore size: the TSU's carbon block has a 0.5-micron rating, while RO membranes have 0.0001-micron pores. This means the TSU removes particulate, chlorine, some lead, and organic compounds but cannot remove dissolved minerals, fluoride, arsenic, nitrate, or TDS. RO systems remove virtually all dissolved substances including beneficial minerals, which is why many RO systems include remineralization stages. The TSU's advantages over RO are: no storage tank (saves cabinet space), no wastewater to drain (1.5 GPM all becomes drinking water versus 1:1 to 1:4 waste ratios for RO), no electricity needed, faster flow rate, simpler installation, and lower upfront and ongoing costs. The disadvantages are: no TDS reduction, no fluoride removal, lower lead reduction (88% vs 99%+), and no independent NSF certification. Choose the TSU for chlorine, taste, and sediment removal in a simple package. Choose RO for comprehensive purification including dissolved contaminants.
Can I install this without drilling any holes?
Yes, with a modification. The TSU ships with a dedicated faucet that requires a 1/2" diameter hole in the sink deck or countertop. If you cannot or will not drill a hole, you have two options. Option 1: Connect the TSU directly to your existing cold water faucet line using a 3-way diverter valve (approximately $12-18 at hardware stores). This diverts cold water through the filter when you pull the diverter lever and sends unfiltered water when the lever is closed. No dedicated faucet needed. Option 2: If your sink has an unused sprayer hole, soap dispenser hole, or cover plate from a previous fixture, the dedicated faucet can install through that existing opening. In our test installation, we used the existing soap dispenser hole with no new drilling. Both approaches make the installation fully reversible for renters.
How do I know when to replace the filter cartridge?
The TSU does not include an electronic filter life indicator. Waterdrop recommends replacement every 6 months or 1,000 gallons, whichever comes first. For most 1-2 person households, the 6-month calendar interval is the limiting factor. Signs that replacement is needed include: reduced water flow at the faucet (indicating carbon block clogging), return of chlorine taste or odor, or visual discoloration of the water. To estimate gallon usage, multiply your household's daily filtered water consumption by the number of days since installation. If two people each drink 0.5 gallons and use 0.5 gallons for cooking daily, that's 2 gallons per day, or 1,000 gallons in 500 days. At that usage rate, the 6-month replacement is appropriate. A family of four using 6 gallons daily would reach 1,000 gallons in 167 days (5.5 months) and should monitor flow rate closely after month 4.
Does the TSU reduce chloramine as well as chlorine?
The TSU's carbon block and post-carbon stages provide some chloramine reduction, but carbon-based filtration is generally less effective at removing chloramine than free chlorine. Chloramine (a compound of chlorine and ammonia used by an increasing number of municipalities) is more stable and requires longer contact time with carbon or catalytic carbon specifically designed for chloramine reduction. In our research with Austin water containing 0.4 ppm chloramine, the TSU achieved approximately 62% chloramine reduction compared to 96% free chlorine reduction. For homes with high chloramine levels (>1.0 ppm), the Aquasana OptimH2O (with catalytic carbon) or a dedicated chloramine filter would be more appropriate. Contact your water utility to confirm whether your supply uses chlorine or chloramine disinfection.
Can the TSU be used with well water?
The TSU can be used with well water that has been tested and confirmed safe for drinking, but with important limitations. The 5-micron PP cotton pre-filter handles moderate sediment loads but will clog quickly in water with high turbidity or sand. The carbon block reduces some organic compounds and improves taste but does not address iron, manganese, hydrogen sulfide (rotten egg odor), hardness, or bacteria. Well water with iron above 0.3 ppm will gradually foul the carbon block, reducing both flow and chlorine removal capacity. Well water with bacterial contamination should not be filtered through the TSU alone; UV sterilization is required. Before installing the TSU on well water, obtain a comprehensive water analysis (available from most county extension offices for $25-50) and address iron, sediment, bacterial, or hardness issues with appropriate upstream treatment.
How does the TSU compare to the Brita under-sink filter and PUR under-sink systems?
The Brita under-sink system (model SAFF-100, $29-39) uses a single carbon block cartridge with 900-gallon capacity and no dedicated faucet. It connects inline to the cold water line and filters all cold water passing through the main faucet. The PUR under-sink system (model PPUFM, $49-59) uses a similar single-cartridge design with 1,000-gallon capacity. Both the Brita and PUR systems cost less upfront but lack the dedicated faucet and 3-stage filtration of the TSU. In our comparative testing, the TSU's 3-stage design (PP cotton carbon block post-carbon) provided 8-12% better chlorine reduction at the end of cartridge life compared to the single-stage Brita and PUR units. The dedicated faucet also prevents filtered water from mixing with unfiltered water at the main tap, which occurs with inline systems when water temperature changes cause backflow. The TSU's 1.47 GPM flow rate exceeded both the Brita (1.1 GPM) and PUR (1.2 GPM) in our research. For the $30-50 price premium, the TSU offers better end-of-life performance, higher flow rate, and a dedicated faucet.
Is the Waterdrop TSU certified by NSF or WQA?
As of October 2024, the Waterdrop TSU does not carry NSF/ANSI or WQA Gold Seal certification for any specific contaminant reduction claims. Waterdrop states that the materials used are FDA-compliant and BPA-free, but independent third-party performance verification is not available. This is common in the sub-$100 filter category, where certification costs ($15,000-50,000 per standard) would significantly impact product pricing. Our independent research provides some validation of performance claims, but buyers should understand that Waterdrop's 96% chlorine reduction and 0.5-micron carbon block specifications are manufacturer-stated, not third-party verified. For buyers requiring certified performance, the Aquasana Claryum under-sink system (NSF 42, 53 certified, $149-179) is the closest certified alternative, though it lacks the TSU's compact tankless design.
Our Methodology
Filter Tested evaluates under-sink water filters through a 90-day residential installation in active households. We measure chlorine reduction using Hach CN-66 total chlorine test kits and Hanna HI711 digital checkers at weekly intervals. Lead reduction is validated through ICP-MS laboratory analysis of spiked water samples. Flow rates are measured using a 1-gallon container and digital stopwatch at the beginning, middle, and end of the test period. Pressure drop is assessed with a digital pressure gauge installed on the inlet line. We evaluate installation procedures by timing DIY installation with standard household tools and assessing reversibility for renters. Build quality is examined through dimensional measurement, materials inspection, and disassembly of spent cartridges. All test units are purchased at retail. Our ratings combine: contaminant reduction performance (40%), flow rate and pressure characteristics (20%), installation and maintenance ease (20%), and total cost of ownership (20%).