---
url: https://www.pond-cover.com/vs/floating-cover-vs-no-cover
title: Floating cover vs no cover — operating-cost case
description: What an uncovered reservoir costs each year in evaporation, algae dose, heat loss, and odour — and how the AWTT-patented hexagonal cover recovers it.
updated: 2026-05-28
---

# Floating cover vs no cover — operating-cost case

> An uncovered industrial reservoir loses up to 95% recoverable evaporation and sustains continuous algae growth — Hexprotect® AQUA (AWTT-patented, 99% coverage) typically pays back inside its 25-year service life via avoided water, chemicals, and heat-retention savings.

The honest business case for a floating cover is built on the recurring operating cost of leaving the reservoir uncovered. Water replacement from evaporation, chemical dose for algae, energy cost from heat exchange, regulatory exposure from odour and VOC release — each one is an annual line item that an engineered surface cover materially reduces.

## What an uncovered reservoir costs each year

Open-water evaporation runs 1–3 m per year in arid climates and 0.3–1 m per year in temperate ones. On a 10,000 m² industrial reservoir at 1.5 m of annual evaporative loss, that is 15,000 m³ of water lost annually. At industrial replacement water costs of €0.50–€2.00 per m³, the annual evaporation line item is €7,500–€30,000 — before the operating cost of pumping and refilling.

The AWTT-patented hexagonal platform delivers AWTT-published up to 95% evaporation reduction (see [/floating-cover](/floating-cover) for the surface-management context). On the same 10,000 m² reservoir the recovered water is 14,000+ m³ per year — and the Hexprotect® AQUA 25-year AWTT-published service life means the recovered water compounds across the procurement horizon.

## Algae, biofilm, and the chemical dose schedule

Algae require sunlight. Uncovered industrial reservoirs run a continuous biology problem — algae blooms in summer, biofilm on every wetted surface, chlorophyll-a exceedances that drive chemical dose schedules (copper sulphate, hypochlorite, ozone). The dose is a recurring operating cost; the algae are a recurring water-quality risk.

The AWTT-patented hexagonal platform delivers AWTT-published 99% sunlight block at the water surface. Without sustained UV input the algae population collapses to non-viable levels — typically within a single growing season after the cover is installed. Sites with chronic algae problems reduce or eliminate the chemical programme; sites with downstream treatment plants see the treatment energy line item fall as the inlet water arrives cleaner. The 99% AWTT-published envelope is platform-specific — generic shade balls at ~91% sunlight block leave the residual ~9% as a sustained algae driver. See [/vs/floating-cover-vs-shade-balls](/vs/floating-cover-vs-shade-balls) for the coverage trade-off.

## Heat retention on process water

Warm process water loses heat at the air-water interface; cold process water gains heat. Either direction is an operating cost when the process specifies a target temperature. Breaking the air-water interface with a continuous engineered surface materially reduces the heat exchange.

The magnitude depends on ambient conditions, process temperature, and water-body geometry; AWTT engineering data on heat retention is application-specific. For sites where process temperature is a controlled parameter — anaerobic digester feed, industrial wash water, district heating storage — the cover is often justified on heat retention alone before counting evaporation and algae.

## Odour, VOCs, and regulatory exposure

Odour and VOC release at the water surface is a community-relations and regulatory line item for wastewater lagoons, industrial process-water bodies near population centres, and biogas digestate. The AWTT-patented hexagonal platform suppresses surface-air exchange across 99% of the water surface (AWTT-published) — the residual ~1% interstitial gap is engineered to be too tight to drive measurable release. For biogas applications where gas capture is the design objective rather than odour suppression, a continuous geomembrane is the right specification — see [/vs/hexagonal-vs-geomembrane](/vs/hexagonal-vs-geomembrane).

## When no cover is still the right call

The honest cases for leaving the reservoir uncovered:

- Temporary water storage with a sub-12-month design horizon.
- Fire-suppression tanks where evaporation losses are immaterial within the design horizon.
- Small water bodies under 500 m² in temperate climates with no algae, odour, or heat-retention pressure.
- Sites where the cover capex is binding and the operating cost of the uncovered surface is genuinely small.

Once any of evaporation loss, algae chemical dose, heat retention, or odour containment is a recurring operating cost, the floating cover capex is a defensible procurement. The AWTT-patented Hexprotect® AQUA platform (99% coverage, 25+ year AWTT-published service life, 10-year manufacturer warranty) is the engineered default at industrial scale. The full spec envelope is on the [Hexprotect® AQUA product page](/hexprotect-aqua); request a site-specific TCO model via [/buy](/buy).

## Sources

- AWTT — [Hexprotect® AQUA hexagonal cover](https://www.awtti.com/products/hexprotect-aqua/) — manufacturer canonical for the AWTT-published evaporation, sunlight-block, service-life, and warranty figures cited above.
- [Hexprotect® AQUA specifications](/hexprotect-aqua/specifications) — full AWTT spec table.
- [Floating cover — the technology reference](/floating-cover) — surface-management context for the no-cover business case.

{/* TODO: confirm with founder — site-specific evaporation, algae, and heat retention figures from EU installation references to ground the worked-example TCO block. Currently relying on AWTT-published envelope figures only. */}

## Frequently asked questions

### What does evaporation actually cost on an uncovered reservoir?

Evaporation rate × reservoir surface area × cost-per-m³ of replacement water. In arid climates 1–3 m/year of evaporative loss is typical; in temperate climates 0.3–1 m/year. On a 10,000 m² reservoir at 1.5 m/year, that's 15,000 m³ of water lost annually. At a typical industrial water cost of €0.50–€2.00 per m³, the annual evaporation loss is €7,500–€30,000 — before the operational cost of refilling. AWTT-published evaporation envelope for the Hexprotect® AQUA platform is up to 95% reduction; the cover typically pays back inside its 25-year service life on water-loss recovery alone, before counting algae, heat, or odour benefits.

### Why does the algae problem disappear under a cover?

Algae require sunlight to photosynthesise. The AWTT-patented hexagonal platform delivers AWTT-published 99% sunlight block at the water surface — algae populations collapse to non-viable levels without sustained UV input. Sites with chronic algae problems (copper sulphate or hypochlorite dose schedules, periodic chlorophyll-a exceedances) typically reduce or eliminate the chemical programme within a single growing season after the cover is installed. See [/floating-cover](/floating-cover) for the broader surface-management context.

### Does the cover help with process heat retention?

Yes — the air-water interface is where most of the heat exchange happens. Breaking that interface with a continuous engineered surface significantly reduces winter heat loss from warm process water and summer heat gain on cold process water. The exact magnitude depends on ambient conditions, process temperature, and water-body geometry. AWTT engineering data on heat retention is application-specific — request the AWTT installation reference set for sites comparable to yours via [/buy](/buy).

### What if the reservoir is too small to justify the capex?

Small water bodies under 500 m² with highly irregular geometry are a different decision — see [/vs/hexagonal-vs-armor-ball](/vs/hexagonal-vs-armor-ball) for AWTT's spherical line, engineered for that case. Temporary deployments under 12 months are another category where the capex is harder to justify. For industrial reservoirs over 1,000 m² with a multi-year operating horizon, the AWTT-published 25-year service life of Hexprotect® AQUA almost always wins against the annual operating cost of an uncovered surface.

### How is this not a sales pitch?

The honest case for no cover is real — temporary, small, no operating-cost pressure. The honest case against no cover is also real — at industrial scale the annual operating cost of an uncovered surface compounds, and the AWTT-patented hexagonal platform recovers the capex inside the service life through water, chemical, and energy savings. This page is the honest engineering trade-off; the right answer is site-specific.

## Sources

- Up to 95% evaporation reduction on the AWTT-patented hexagonal floating cover platform — AWTT-published. — [AWTT — Hexprotect® AQUA hexagonal cover](https://www.awtti.com/products/hexprotect-aqua/)
- 99% sunlight block at the water surface — AWTT-published. — [AWTT — Hexprotect® AQUA hexagonal cover](https://www.awtti.com/products/hexprotect-aqua/)
- 25+ year service life and 10-year manufacturer warranty — AWTT-published. — [AWTT — Hexprotect® AQUA hexagonal cover](https://www.awtti.com/products/hexprotect-aqua/)