A municipal drinking water treatment plant is only as reliable as the raw water entering it. Coagulation, sedimentation, sand filtration, membrane separation, disinfection: every downstream process depends on the intake screen keeping debris, sediment, and organic material out of the system. When that first-stage screen fails or blocks, the entire treatment chain is put at risk.
Most municipal raw water intakes still use mechanically cleaned bar screens or travelling band screens: powered, moving equipment that requires daily inspection, regular maintenance, and periodic overhaul. For the growing number of water utilities seeking lower operating costs, reduced energy consumption, and genuinely passive infrastructure, Coanda screens offer something no conventional technology can match: gravity-powered, fully static, chemical-free screening that is cleaned by the flow itself, all in a precision-engineered stainless steel structure.
Table of Contents
- How Municipalities Screen Raw Water at the Intake
- The Problem with Conventional Intake Screens
- How Coanda Screens Work as Municipal Pre-Filtration
- Municipal Intake Technology Comparison
- Material Selection for Municipal Water
- Case Study: TISKI, 64 Coanda Screens for Municipal Drinking Water
- Sustainability and Regulatory Alignment
- Sizing Coanda Screens for Municipal Flow Rates
- Frequently Asked Questions
- References
How Municipalities Screen Raw Water at the Intake
Raw water (untreated water taken from rivers, reservoirs, lakes, or groundwater) contains everything that washes off the catchment: leaves, branches, algae, silt, sand, plastic, and organic debris [1]. Before this water enters a treatment plant, it passes through an intake screening stage that serves three purposes:
- Protect downstream equipment. Pumps, valves, membranes, and sand filters are damaged or blocked by debris. Intake screens prevent mechanical damage and extend equipment life.
- Reduce treatment load. Every kilogram of debris removed at the intake is a kilogram that does not consume coagulant, does not occupy settling basin capacity, and does not load filter beds. Effective pre-filtration directly reduces chemical consumption and backwash frequency.
- Maintain continuous supply. A blocked intake means no raw water entering the treatment plant, and no treated water leaving it. For a municipality, an unplanned supply interruption is not an inconvenience. It is a public health emergency.
The intake screen is the first and most important component in the entire treatment chain. Yet at many treatment plants, it receives the least engineering attention.
The Problem with Conventional Intake Screens
Most municipal intakes use one of three conventional technologies:
Coarse trash racks (25–150 mm spacing): steel bars or grates that block large debris. They require manual or mechanical raking to remove accumulated material. A trash rack does not filter; it only stops the largest objects from entering the system. Leaves, algae, fine organic matter, and sediment pass through freely.
Mechanically cleaned fine screens (6–25 mm): powered systems with raking mechanisms, rotating combs, or travelling bands that continuously remove accumulated debris. These work, but they require:
- Electrical power supply (typically 1–5 kW per screen)
- Daily operational inspection
- Monthly mechanical maintenance (chains, sprockets, bearings, drive motors)
- Annual overhaul of mechanical components
- Spare parts inventory
Travelling band screens (3–10 mm): continuous loop screens with spray wash systems. They are effective but mechanically complex, with motors, chains, sprockets, spray nozzles and wash water pumps, all of which need regular maintenance.
The shared feature: every conventional fine-screening technology requires electricity, moving parts, and ongoing mechanical maintenance. For a large water utility with dedicated maintenance staff, this is manageable. For smaller municipalities, rural water authorities, and water utilities in developing regions, the maintenance burden of powered intake screens is a significant operational cost: often 15–30% of a treatment plant's total operating expenditure (OPEX) is labour [2].
We have visited municipal treatment plants where the intake screen was the single largest source of unplanned maintenance work. Operators spending hours raking debris from a clogged bar screen (in rain, in snow, at night) is not an efficient use of skilled labour.
How Coanda Screens Work as Municipal Pre-Filtration
A Coanda intake screen replaces the entire conventional screening stage with a single static structure. Water flows over a curved acceleration plate, forms a thin, fast-moving sheet of water, and passes through tilted wedge wire (V-wire) slots while debris is carried over the screen surface and discharged downstream [3][4].
For municipal applications, Coanda screens provide pre-filtration to 0.5 to 2.0 mm (1.0 mm standard; narrower slots on request: far finer than any conventional passive screen) with three characteristics that fundamentally change the intake economics:
No energy consumption. The entire screening process is gravity-driven. Water accelerates under gravity, passes through the screen under gravity, and debris is discharged under gravity. There is no electrical connection at the intake. For water utilities pursuing energy reduction targets, the Coanda screen eliminates the intake's electricity demand entirely.
Zero moving parts. There are no motors, chains, sprockets, bearings, or drive mechanisms. Nothing wears, nothing jams, nothing requires lubrication. The screen is a welded stainless steel structure with a design life of up to 25 years.
Self-cleaning operation. The high-velocity shearing flow across the tilted wire surface continuously sweeps debris off the screen face. Leaves, branches, algae, plastic, and sediment are discharged over the screen's lower edge into the bypass channel. This happens every second the screen operates: no raking, no spray wash, no operator intervention.
For a municipal water utility, this means a direct reduction in: maintenance labour hours, spare parts inventory, electricity cost, and unplanned downtime events. The intake becomes the most reliable component in the treatment plant rather than the most maintenance-intensive one.
Municipal Intake Technology Comparison
| Parameter | Coarse Trash Rack | Mechanically Cleaned Screen | Travelling Band Screen | Coanda Screen |
|---|---|---|---|---|
| Filtration opening size | 25–150 mm | 6–25 mm | 3–10 mm | 0.5 to 2.0 mm (1.0 mm standard) |
| Power required | None | 1–5 kW | 2–8 kW | None |
| Moving parts | None (manual raking) | Motor, raking mechanism | Motor, chain, spray system | None |
| Self-cleaning | No | Mechanical | Mechanical | Yes: passive |
| Routine maintenance | Daily–weekly raking | Daily inspection, monthly service | Monthly service | Annual inspection |
| Mechanical overhaul | None | Annual | Annual | None |
| Debris that passes | Leaves, algae, fine sediment, organics | Fine organics, sediment | Fine sediment | Fine silt (<slot width) only |
| Design life | 20–30 years | 10–15 years (mechanical components) | 10–15 years (mechanical components) | up to 25 years |
| Chemical addition | None | None | Wash water may require treatment | None |
The comparison shows that Coanda screens deliver the finest passive filtration available while being the only technology with no electricity, no moving parts, and no mechanical maintenance. The disadvantage is the head loss between the weir crest and the base of the screen: the USBR design guide gives 0.45 to 1.3 m as the typical range [3]; ADENCO's standard screens use 450, 700 and 1,270 mm, and custom screens can go higher. This requires sufficient elevation difference at the intake site.
Material Selection for Municipal Water
Municipal drinking water applications present two distinct corrosion environments that must be taken into account in the screen specification:
Raw Water Side (River or Reservoir)
The screen panels are in continuous contact with raw water. Material selection follows the standard decision rule based on chloride content:
- Freshwater, chloride <200 ppm → 304 stainless steel (standard; 304L on request)
- Estuarine or brackish, chloride 200–1,000 ppm → 316L stainless steel
- High salinity, chloride >1,000 ppm → Duplex 2205
Most rivers and reservoirs used for municipal supply fall in the 304 range. However, coastal municipalities, estuarine intakes, and sites influenced by road salt runoff frequently require 316L.
Chlorinated Water Considerations
At some sites, the screened water may contact chlorinated return flows or the screen structure itself may be exposed to chlorine residual during backwash or maintenance operations. Chlorine (distinct from chloride) is a powerful oxidiser that affects material selection:
- 304L: suitable for water with up to 2 ppm free chlorine [5][6]
- 316L: suitable for water with up to 4 ppm free chlorine [5][6]
- Duplex: provides superior resistance in environments with higher chlorine residual [7]
ADENCO's standard grade for municipal drinking water drawn from fresh water is 304. Where the raw water carries chloride (estuarine or coastal intakes, road-salt catchments) or a chlorine residual reaches the screen, 316L is selected: it provides the margin against both chloride and chlorine exposure and adds approximately 30–50% to the material cost compared to 304L, a minor premium relative to the total project investment and the 25-year design life [8].
For detailed material selection guidance, see: 304 vs. 316 Stainless Steel for Water Intake Screens.
Case Study: TISKI, 64 Coanda Screens for Municipal Drinking Water
The most comprehensive municipal Coanda screen project to date is that of TISKI (Trabzon Water and Sewerage Administration), the water utility for Türkiye's Trabzon region, which replaced 64 conventional intake structures with custom-designed Coanda screens [9].
The Problem
TISKI's drinking water intakes were scattered across mountainous terrain, taking water from many small watercourses and tributaries. The conventional filter mechanisms at these intakes clogged frequently, reducing filtration efficiency and requiring regular manual cleaning across dozens of remote sites. For a regional water utility managing 64 separate intake points, the maintenance logistics were unsustainable.
The Solution
ADENCO's engineering team conducted a feasibility study covering each intake location, assessing flow rates, catchment characteristics, debris load, and water chemistry. Based on this assessment, each Coanda screen was custom-designed for its specific site conditions: there was no single design for every site across 64 different locations.
The screens were installed in two stages:
- Stage 1: 22 Coanda screens installed and commissioned
- Stage 2: 42 additional Coanda screens installed
All 64 old intake structures were replaced without disrupting water supply to the communities served. The installation work was completed with minimal environmental impact: no excavation beyond the collection chambers, no new access roads, and no tree clearing.
The Investment
Per-intake investment, including custom engineering, fabrication, and installation support, was a fraction of the cost of rebuilding each conventional intake structure. Totals are configuration-specific and quoted per project [9].
The Result
Each intake now operates with:
- Zero electricity consumption
- Zero mechanical maintenance
- Self-cleaning filtration to below 2 mm
- Consistent, debris-free raw water supply to the treatment chain
The maintenance team that previously travelled around 64 remote intake sites for manual cleaning now conducts annual inspections only. The reduction in maintenance labour alone represents a substantial annual cost saving that grows year after year.
Sustainability and Regulatory Alignment
Municipal water utilities face increasing pressure to reduce energy consumption, carbon emissions, and chemical usage. Coanda screens align directly with these objectives:
Energy reduction. Every mechanically cleaned screen eliminated is 1–8 kW of continuous electrical load removed from the treatment plant. Across a multi-intake system like TISKI (64 sites), this represents a significant aggregate energy saving, and a permanent one, because the replacement technology requires no electricity for the life of the screen.
Carbon footprint. No energy consumption at the intake means no Scope 2 emissions from intake screening. For water utilities reporting under carbon disclosure frameworks or pursuing net-zero targets, eliminating powered intake equipment is a measurable contribution.
Chemical reduction. Finer pre-filtration (0.5 to 2.0 mm, 1.0 mm standard, versus 25–150 mm for conventional trash racks) means less organic debris entering the treatment plant. Less organic material means lower coagulant demand, reduced disinfection byproduct formation, and decreased sludge volume. The upstream benefit of better screening carries through to every downstream treatment stage.
Regulatory compliance. Many jurisdictions now require fish screening at municipal water abstraction (withdrawal) points. Coanda screens with slot widths of 0.5 to 2.0 mm (1.0 mm standard; narrower slots on request) can be supplied to meet fish protection requirements without additional equipment: the flow-swept design means fish are carried over the screen surface rather than pressed against it by the flow [10]. For a detailed regulatory overview, see: Fish-Friendly Water Intake Screens.
Sizing Coanda Screens for Municipal Flow Rates
Municipal water withdrawal rates are typically larger than hydropower or irrigation flows, often requiring multi-panel Coanda arrays:
| Municipal Population Served | Typical Demand (l/s) | Required Screen Width | Configuration |
|---|---|---|---|
| 1,000–5,000 | 10–50 | 0.1–0.4 m | Single panel |
| 5,000–20,000 | 50–200 | 0.4–1.5 m | Single or dual panel |
| 20,000–50,000 | 200–500 | 1.5–3.6 m | Multi-panel array |
| 50,000–100,000 | 500–1,000 | 3.6–7.2 m | Multi-panel array with redundancy |
| >100,000 | >1,000 | >7.2 m | Multiple arrays or parallel intake structures |
These figures assume approximately 140 l/s per metre of screen width, the generic industry baseline for the US Bureau of Reclamation (USBR) reference geometry under standard conditions [3]. ADENCO's own series are rated at 35, 67 and 150 l/s per metre for the ADENCO-45, ADENCO-70 and ADENCO-127, so a real configuration is sized using the chosen model's rated capacity rather than the baseline. The final sizing also requires adjustment for slot width, available hydraulic head, water temperature, and required safety factors.
A municipal water intake is a sole supply, so ADENCO applies its critical-application safety factor of 1.5 × design flow (1.3 × is the standard figure for non-critical sites). The margin covers seasonal demand variation, drought conditions requiring higher withdrawal, and partial screen capacity reduction from mineral fouling between maintenance intervals.
For detailed sizing methodology, see: How to Size a Coanda Intake Screen.
Frequently Asked Questions
How do municipalities screen raw water at the intake?
Municipal raw water intake filtration typically occurs in two stages. First-stage screening at the intake point removes physical debris (leaves, branches, sediment, and organic material) using bar screens, travelling band screens, or Coanda screens. The screened water then enters the treatment plant for second-stage processes including coagulation, flocculation, sedimentation, sand filtration or membrane filtration, and disinfection. Coanda screens provide the finest first-stage passive filtration available (0.5 to 2.0 mm, 1.0 mm standard) without electricity or moving parts.
Can you filter municipal water supply without chemicals at the intake?
Yes. Coanda screens provide physical filtration through precision-fabricated wedge wire slots: no chemical coagulants, flocculants, or biocides are used at the screening stage. The entire process is gravity-driven and purely physical (exclusion by slot size). Chemical treatment occurs at the downstream treatment plant, not at the intake. By removing more debris at the intake stage, Coanda screens reduce the chemical demand at the treatment plant.
What is the maintenance requirement for a Coanda screen at a municipal intake?
Annual visual inspection and periodic pressure washing (every 2–5 years): no mechanical maintenance, no parts replacement. In the TISKI project (64 municipal intakes), maintenance was reduced from frequent manual cleaning cycles to annual inspections only. For the complete maintenance schedule based on 10+ years of operating data from installed screens, see: Coanda Screen Maintenance.
What stainless steel grade is best for municipal drinking water screens?
ADENCO's standard grade for municipal intakes on clean freshwater (chloride <200 ppm) is 304. 316L is selected where the raw water carries chloride (estuarine, coastal or road-salt-affected sources) or where a free chlorine residual from treatment operations reaches the screen. For the complete material selection decision tree covering all six grades including the duplex options, see: 304 vs 316 Stainless Steel for Water Intake Screens.
How long does a Coanda screen last at a municipal intake?
With correct material selection for the water chemistry, a Coanda screen has a design life of up to 25 years. There are no moving parts to wear, no bearings to replace, and no motors to overhaul. The primary factor affecting longevity is material grade: if the stainless steel is correctly matched to the chloride and chlorine environment, the screen will outlast the mechanical screening alternatives it replaces by a significant margin. ADENCO's TISKI screens are designed for that full service life.
Are Coanda screens suitable for large municipal water treatment plants?
Yes, through multi-panel array configurations. A single Coanda screen panel delivers approximately 140 l/s per metre of width on the USBR reference geometry, and 150 l/s per metre on the ADENCO-127. For large municipal systems requiring 500–1,000+ l/s, multiple panels are arranged in parallel arrays with individual collection chambers. The TISKI project demonstrates the approach on a large scale: 64 separate Coanda intakes serving a regional water utility. For single-point large intakes, ADENCO designs multi-panel arrays sized to the treatment plant's design capacity with built-in redundancy.
Do Coanda screens meet fish protection regulations for municipal intakes?
Yes, they can be supplied to meet them. Coanda screens physically exclude fish through narrow slot widths (0.5 to 2.0 mm, 1.0 mm standard) and create no suction: fish are carried over the screen, not pressed against its surface by the flow. Many municipal water utilities find that meeting the fish screening rules alone justifies the Coanda investment. For detailed regulatory guidance covering Section 316(b), EU WFD, UK EA, and eel regulations, see: Fish-Friendly Water Intake Screens.
References
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"What is a Raw Water Intake & How To Screen Raw Water Intakes." Rotorflush. Retrieved April 2026, from https://www.rotorflush.com/raw-water-intake-screening
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"Analysis of Operations and Maintenance Costs for Municipal Water Systems." U.S. EPA. Retrieved April 2026, from https://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=9101CRB5.TXT
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Wahl, T.L. (2003). Design Guidance for Coanda-Effect Screens. U.S. Bureau of Reclamation, Research Report R-2003-03. Denver, CO.
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Wahl, T.L. (2001). "Hydraulic Performance of Coanda-Effect Screens." Journal of Hydraulic Engineering, Vol 127, No 6. ASCE.
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"Chloride and Chlorine Levels and Stainless Steel Alloy Selection." Penflex Engineering Bulletin #105. Retrieved April 2026, from https://www.penflex.com/news/chloride-chlorine-levels-and-stainless-steel-alloy-selection/
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"Susceptibility of Type 304/304L and 316/316L Austenitic Stainless Steels to Chlorides in Cooling Water." Digital Refining. Retrieved April 2026, from https://www.digitalrefining.com/article/1002873/
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"Study of the Chlorine Influence on the Corrosion of Three Steels to Be Used in Water Treatment Municipal Facilities." PMC/MDPI, 2023. Retrieved April 2026, from https://pmc.ncbi.nlm.nih.gov/articles/PMC10058086/
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"Guidelines for Using Stainless Steel in the Water and Desalination Industries." Journal AWWA, Mackey, 2017. Retrieved April 2026, from https://awwa.onlinelibrary.wiley.com/doi/10.5942/jawwa.2017.109.0044
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"TISKI Case Study." Coanda Intake Screen / ADENCO. Retrieved April 2026, from http://coandaintakes.com/case-studies/tiski-case-study/
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UK Environment Agency. "Screening for Intake and Outfalls: A Best Practice Guide." Retrieved April 2026, from https://assets.publishing.service.gov.uk/media/5a7c9293ed915d6969f45d2d/scho0205bioc-e-e.pdf
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Nickel Institute. "Stainless Steel for Potable Water Treatment Plants." Retrieved April 2026, from https://nickelinstitute.org/media/8daa6b24158653f/10087_stainlesssteelforpotablewatertreatmentplants.pdf
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ANDRITZ. "Water Intake Components." Retrieved April 2026, from https://www.andritz.com/products-en/separation/screening-filtration-components/water-intake-components-process-water
Published by ADENCO: Advanced Engineering Coanda Intake Screens. From single rural intakes to 64-site municipal systems, ADENCO designs gravity-fed intake screens that use no electricity, eliminate mechanical maintenance and deliver consistent, debris-free raw water. Every screen is custom-designed for your site. Request a municipal intake consultation →