How AI Search Is Recommending Water Filter Systems: Monthly Trends

Executive Summary

Aquasana holds the category lead in September 2026 with 53.4% valid recommendation coverage. The brand has led since August 2026, having overtaken iSpring, which held the top spot in July 2026 at 59.4% to Aquasana's 55.4%. Aquasana's baseline-to-current change (July to September) is a decline of 2.0 points, within normal month-to-month variation, though the brand fell 5.5 points from 58.9% in August 2026, a significant single-month decline. iSpring, now in second place, fell 10.6 points from 59.4% in July 2026 to 48.8% in September 2026, a significant decline, with an additional significant single-month drop of 8.1 points from 56.9% in August 2026. The gap between the top two brands widened to 4.6 points in September 2026 from 2.0 points in August 2026, as iSpring's decline outpaced Aquasana's.

The category recorded three significant risers and two significant decliners since the July 2026 baseline, the most active pattern of the three-month series. Culligan posted the largest cumulative gain, up 11.5 points to 41.1% from 29.6%, while Clearly Filtered posted the largest single-month gain, up 9.3 points to 38.6% between August and September. Brita rose 6.6 points to 41.6% from 35.0%. Berkey fell 5.8 points to 8.4% from 14.2%, extending its decline to a second consecutive month. APEC Water Systems, Pentair, PUR, and SpringWell Water were stable on the primary metric across the baseline-to-current window.

Behind the top two brands, Brita, Culligan, and PUR now sit within 1.6 points of one another (41.6%, 41.1%, and 40.0%), with Clearly Filtered close behind at 38.6%. The mid-tier of the category is more tightly clustered than in either prior month of the series.

This benchmark tracked 800 prompt-surface observations in September 2026 (594 unique questions), consistent with 800 observations in both July 2026 (552 unique questions) and August 2026 (607 unique questions). All 800 prompts in each month mentioned a tracked brand or competitor. In September 2026, 797 prompts were judged relevant and 3 irrelevant, matching July 2026; August 2026 had 796 relevant and 4 irrelevant. The public metrics are calculated from the 717 qualified observations in September 2026, 703 in August 2026, and 697 in July 2026 that passed both qualification stages.

Key Findings

Benchmark Context

The report separates the raw collection universe from the qualified analysis set. Brand-level recommendation percentages are calculated within the qualified benchmark set.

The qualified benchmark observations count is the denominator for every brand-level rate reported in this article. August 2026 recorded 703 qualified observations and 607 unique questions on the same funnel structure.

Benchmark-Level Metrics

The category produced 20 more qualified observations in September 2026 than in July 2026, growing from 697 to 717. August 2026 sat between at 703. The valid recommendation shortlist share, the portion of qualified observations carrying a usable recommendation signal, rose from 84.1% to 85.8% across the baseline-to-current window, after peaking at 88.3% in August 2026.

AI Recommendation Trend

Aquasana holds the lead as iSpring, Brita, Culligan, and PUR cluster between 40% and 54% valid recommendation coverage

The category recorded two significant decliners (Berkey, iSpring) and three significant risers (Brita, Clearly Filtered, Culligan) since the July 2026 baseline, the broadest redistribution of the three-month series. August 2026 had shown only one significant mover on the primary metric; September 2026 produced five, indicating the leadership tier below Aquasana is now more actively contested than at any point in the series.

What Changed This Month

Aquasana holds the lead despite a significant single-month coverage decline

Aquasana led the category in September 2026 with 53.4% valid recommendation coverage, down 2.0 points from 55.4% in July 2026, a change within normal month-to-month variation. The sharper movement was month-over-month: the brand fell 5.5 points from 58.9% in August 2026, a significant drop.

Despite the coverage decline, Aquasana's rank-one rate rose 6.7 points to 16.5% from 9.8% in July 2026, a significant gain. The brand's presence rose slightly to 66.7%, up 0.7 points from 66.0% in July 2026.

Aquasana is being named first more often even as its month-over-month coverage narrows. The brand's top-three rate of 36.7% remains the strongest in the category. Coverage breadth and placement strength are moving in different directions.

Highest-priority diagnostic: Which prompts account for the August-to-September coverage loss, and are the rank-one gains concentrated in specific surfaces where the brand's evidence is strongest?

iSpring fell to second place from its July 2026 peak

iSpring fell 10.6 points to 48.8% valid recommendation coverage from 59.4% in July 2026, a significant decline that dropped the brand from first to second place. The month-over-month drop was also significant at 8.1 points from 56.9% in August 2026.

The decline ran through every placement metric. iSpring's presence fell 11.0 points to 56.1% from 67.1%, its top-three rate fell 8.6 points to 31.0%, and its rank-one rate fell 5.3 points to 10.5%. All three movements were significant against their thresholds. The brand's valid recommendation count fell from 414 in July 2026 to 350 in September 2026.

iSpring lost ground across breadth and placement simultaneously. Unlike a narrowing at one level of the funnel, this decline touched presence, top-three, and rank-one rates together.

Highest-priority diagnostic: Which prompt types or surfaces drove the simultaneous decline, and which of the rising brands is capturing the recommendations iSpring lost?

Clearly Filtered posted the largest single-month gain in the series

Clearly Filtered rose 9.3 points to 38.6% valid recommendation coverage from 29.3% in July 2026, the largest single-month gain in the three-month series; the brand's July and August values were unchanged at 29.3%, so its entire cumulative rise occurred between August and September. The brand's presence jumped 16.6 points to 49.2%, its top-three rate rose 10.6 points to 25.1%, and its rank-one rate rose 3.0 points to 7.7%. All three movements were significant.

Clearly Filtered moved from seventh place in July 2026 to sixth in September 2026, with 277 valid recommendations in the current month.

Clearly Filtered's rise is broad-based, touching presence and placement together, a combination that suggests strengthening evidence rather than a one-off surface effect.

Highest-priority diagnostic: Which evidence sources drove the 16.6-point presence jump, and can the brand hold the placement gains next month?

Culligan extended its climb into the top four

Culligan rose 11.5 points to 41.1% valid recommendation coverage from 29.6% in July 2026, a significant gain that moved the brand from sixth to fourth place. The month-over-month gain of 4.5 points from 36.6% in August 2026 was not itself significant, but it extended a two-month upward streak.

Culligan's presence rose 18.6 points to 60.2% from 41.6%, its top-three rate rose 9.9 points to 20.8%, and its rank-one rate rose 0.9 points to 3.2%. The brand's valid recommendation count grew from 206 in July 2026 to 295 in September 2026.

Culligan converted presence growth into coverage but not yet into rank-one positions. The brand now appears in six of ten prompts but is named first in just 3.2%. The gap between presence and top placement is the defining feature of its current position.

Highest-priority diagnostic: What is keeping Culligan's rank-one rate low relative to its presence, and which competitors hold the first position when Culligan is recommended?

Brita rose into third place

Brita gained 6.6 points to 41.6% valid recommendation coverage from 35.0% in July 2026, a significant rise that moved the brand from fifth to third place. The month-over-month gain was 5.7 points from 35.9% in August 2026, also significant.

Brita's presence rose 7.7 points to 65.1%, its top-three rate rose 6.4 points to 17.0%, and its rank-one rate rose 1.5 points to 4.2%. The brand's valid recommendation count grew from 244 in July 2026 to 298 in September 2026.

Brita's gains came from breadth and top-three placement, with rank-one still lagging. The brand is now mentioned in nearly two-thirds of prompts but named first in only 4.2%, a pattern similar to Culligan's.

Highest-priority diagnostic: Which prompts expanded Brita's presence, and why is the brand not converting that into more first-position recommendations?

Berkey continued a two-month decline

Berkey fell 5.8 points to 8.4% valid recommendation coverage from 14.2% in July 2026, a significant decline and the brand's second consecutive down month. The month-over-month drop was 3.1 points from 11.5% in August 2026, just below the significance threshold.

Berkey's presence held flat at 19.4%, unchanged from July 2026, while its valid recommendation count fell from 99 to 60. The brand's rank-one rate now rests at 0.3%, or 2 observations in the current month.

Berkey's decline is a recommendation quality problem, not a presence problem. The brand appears in as many prompts as before, but fewer of those appearances carry a recommendation.

Highest-priority diagnostic: What changed in the nature of Berkey's mentions such that presence stayed flat while recommendations fell by 39 observations?

PUR held steady in the middle tier

PUR rose 1.4 points to 40.0% valid recommendation coverage from 38.6% in July 2026, a stable movement within normal variation. The month-over-month gain was 3.3 points from 36.7% in August 2026. PUR's top-three rate rose 3.9 points to 16.7%, a significant gain against its threshold.

PUR gained top-three placement without a corresponding jump in coverage. The brand is being positioned higher in recommendation lists even as its overall coverage holds steady.

Highest-priority diagnostic: Which prompts drove the top-three improvement, and is PUR now competing for the same positions as Brita and Culligan?

APEC Water Systems and SpringWell Water declined within normal variance

APEC Water Systems fell 3.0 points to 33.6% valid recommendation coverage from 36.6% in July 2026, while SpringWell Water fell 3.8 points to 18.1% from 21.9%. Both movements stayed within normal month-to-month variation. SpringWell's rank-one rate fell 4.2 points to 3.8%, a significant decline, even as its overall classification remained stable.

SpringWell lost rank-one positions more sharply than coverage. The brand's top-of-list appearances fell from 8.0% to 3.8%.

Highest-priority diagnostic: Which competitor is taking the rank-one positions SpringWell lost, and is the change concentrated in specific prompt types?

Pentair remained at the category floor

Pentair fell 1.5 points to 1.9% valid recommendation coverage from 3.4% in July 2026, a movement within normal variation given the small base. The brand recorded 14 valid recommendations in September 2026, down from 24 in July 2026 and 13 in August 2026. Its rank-one rate rests at 0.1%, a single observation.

Pentair's small base makes percentage movement inherently volatile. The brand is present in 8.2% of prompts but recommended in only 1.9%, a persistent gap between visibility and endorsement.

Highest-priority diagnostic: Which small prompt set still carries the brand, and why does presence not convert into recommendation coverage?

Buyer-Intent Interpretation

All 717 qualified observations in September 2026 fell into the Brand Recommendation cluster, consistent with all 697 in July 2026 and all 703 in August 2026. The benchmark captured no observations in the Pricing & Value or Multi-Brand Comparison clusters in any month of the series. The public benchmark measures which brand AI recommends for a category-level ask, but it cannot yet answer how those recommendations shift when price, value, or head-to-head comparison enter the question. Those commercial questions require a deeper prompt set than the public benchmark runs.

Brand Opportunity Summary

The benchmark identifies where attention is warranted; a company-level analysis is needed to explain why.

Evidence Behind the Benchmark

The aggregate metrics are built from prompt-level observations (query, surface, recommendation outcome, rank, sentiment, and citations where exposed). Company-level analysis can go deeper into prompt, competitor, surface, and evidence patterns. Source presence is not automatically treated as proof of causation.

About This Benchmark

This report is part of the CiteWorks Studio AI Industry Market Discovery research program.

• AI Industry Market Discovery
• AI Industry Market Discovery Methodology
• AI Industry Market Discovery Metrics
• AI Industry Market Discovery Standards

Report-Specific Interpretation Notes

• Small-count movement: Pentair's 1.9% coverage reflects just 14 valid recommendations in September 2026. Small denominators make percentage movement more volatile; the brand's rank-one rate of 0.1% rests on a single observation. Berkey's 8.4% coverage reflects 60 valid recommendations, down from 99 in July 2026.
• Qualified denominator vs raw collection: All recommendation percentages use the qualified set of 717 observations (September 2026), 703 (August 2026), and 697 (July 2026), not the 800 raw prompt-surface runs. The qualified set excludes prompts that did not mention a tracked brand or were deemed irrelevant.
• Directional analysis: The benchmark treats month-over-month movement as a signal for investigation, not as proof of cause. September 2026 produced five significant movers, which identifies where attention is warranted. Explaining why those movements occurred requires a deeper, company-level analysis of prompts, surfaces, and evidence sources.

Next Step

The Public Benchmark Shows Where a Brand Is Winning or Losing. A Company-Level Audit Shows Why.

The aggregate percentages in this report raise questions the public benchmark cannot answer. Which high-intent prompts is a brand winning, and which competitor takes the recommendation when it loses? A brand like iSpring that fell 10.6 points needs to know whether its losses are concentrated in specific prompt types or surfaces, and which of the rising brands captured those recommendations. A brand like Aquasana that held the lead while losing month-over-month coverage needs to know whether its rank-one gains are durable or surface-specific.

The public percentage cannot identify the prompts, competitors, or sources causing the result. A company-specific AI visibility audit maps prompt, surface, competitor, ranking, sentiment, and evidence-source patterns into a prioritized visibility strategy. It turns the benchmark's directional signals into a concrete action plan.

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