Saving Water with Aquaponics: Recirculation, Losses and Real Environmental Impact

Circulation does not mean zero water consumption

Aquaponics combines fish farming and crop production in a largely recirculating water system. After mechanical and biological treatment, the water is passed through fish tanks, filters and plant areas again.

This means that new water does not have to be provided for every irrigation process. However, the system is not completely closed. Water leaves the facility through evaporation, plant transpiration, crop products, filter cleaning, maintenance and minor technical losses.

The environmental benefits of an aquaponics system must be measured. A water cycle alone does not prove overall sustainable production.

1. Record the operational water balance

Water consumption should not be derived from the pool volume. What matters is how much water is actually refilled during the period under consideration.

Refill water = evaporation + plant transpiration + cleaning losses + withdrawals + leaks

For a reliable water balance, at least the following values are documented:

  • Filling quantity during commissioning,
  • water refilled daily or weekly,
  • water taken for filter cleaning,
  • specifically exchanged water,
  • amount of fish and plants harvested,
  • Production time.

Automatic make-up is practical, but can mask unnoticed leaks. A water meter in the refill line makes the actual consumption visible.

2. Relate water consumption to production

An absolute consumption value means little if the quantity produced is not known. Therefore, the water requirement should be based on a product or a production area.

Water intensity = refill water used ÷ salable product quantity

For example, consumption can be reported separately as:

  • liters of water per kilogram of vegetables,
  • liters of water per head of lettuce,
  • liters of water per kilogram of fish,
  • Liters of water per square meter and production cycle.

In the case of combined fish and plant production, it must be transparently documented how the shared water consumption is distributed between both product groups.

3. Distinguish between evaporation and transpiration

Evaporation is the loss of water from open water surfaces, pipes or moist surfaces. Transpiration is the release of water by plants through their leaves. Both processes are influenced by temperature, humidity, air movement and radiation.

Evaporation losses can be reduced by, among other things:

  • Covers on unneeded water areas,
  • tight pipes and closed returns,
  • regular checks for leaks,
  • adapted air flow,
  • suitable insulation and shading.

Plant transpiration, on the other hand, is part of their growth and cannot be completely avoided. It changes with crop type, leaf area and development stage.

4. Use rainwater as a supplement

Captured rainwater can reduce the need for tap or well water. However, roofing material, collection area, storage, contamination and water quality must be checked before use.

A simple estimate of the theoretically available rainwater is:

Yield in liters = precipitation in millimeters × roof area in square meters × runoff coefficient

One millimeter of precipitation per square meter is equivalent to one liter of water. In practice, losses occur through evaporation, overflow, filtering and the first dirty roof drain.

Rainwater often has only a small buffering capacity. The pH value and carbonate hardness must therefore be checked before and during use.

5. Keep nutrients in the system

Fish feed is the most important external source of nutrients in an aquaponics system. Only some of the substances contained are converted directly into fish biomass. Other components enter the water cycle as dissolved compounds or solids.

Good solids separation prevents deposits, but must not result in nutrient-rich sludge being disposed of in an uncontrolled manner. Depending on hygienic and legal requirements, separated solids can be treated, mineralized or tested for other suitable recycling routes.

Regular complete water replacement would lose water and nutrients at the same time. The causes of problematic water values ​​should therefore first be determined before large amounts of water are replaced.

6. Monitor nitrogen losses and water quality

In the biofilter, ammonium or ammonia is converted into nitrate via nitrite. Plants absorb some of the nitrate. If nutrient production remains permanently higher than plant uptake, nitrate can accumulate.

Important control values are:

  • ammonium or ammonia,
  • nitrite,
  • nitrate,
  • pH value,
  • dissolved oxygen,
  • electrical conductivity as a supplementary trend value.

Increasing values can indicate unbalanced feeding, too few plants, insufficient filter performance or a disruption in biological processes.

7. Include energy needs in the environmental assessment

Water savings should not be viewed in isolation from energy requirements. Pumps, ventilation, controls, heating, cooling and artificial lighting can have a major impact on the environmental footprint.

The power requirement of a continuously operated component is calculated with:

Power consumption = power in kilowatts × operating hours

Efficient pumps, low delivery heads, sufficiently dimensioned pipes and short pipe routes reduce energy requirements. Unnecessarily throttling large pumps permanently wastes electricity.

For heated or illuminated systems, it should also be checked whether waste heat, photovoltaics, seasonal production or an adapted choice of crops can reduce the energy requirement.

8. Consider the environmental impact of fish feed

The environmental impact of fish production depends largely on the feed used. Raw materials, processing, transport, protein content and feed utilization influence resource requirements.

Important operational metrics are:

  • amount of feed used,
  • increase in fish biomass,
  • feed losses,
  • Origin and composition of the feed,
  • Proportion of utilized and excreted nutrients.

Overfeeding not only worsens economic efficiency, but also increases oxygen consumption, the amount of solids and the load on the biofilter.

9. Evaluate materials and lifespan

Pools, pipes, pumps, filter media and greenhouse components require raw materials and energy for production and transport. Long-lasting, repairable components that are suitable for the intended purpose improve the environmental balance.

When choosing materials, the following are important:

  • Suitability for drinking water or food contact,
  • resistance to UV radiation and moisture,
  • Repairability and available spare parts,
  • expected useful life,
  • Possibility of reuse or recycling.

Used containers may only be used if their previous use is known and there are no problematic residues.

10. Control wastewater and overflows

A recirculating system can also release water during cleaning, heavy rain, maintenance or technical malfunctions. Overflows and drains must be planned so that nutrient-rich water does not flow uncontrollably into the ground, sewers or surface waters.

Before discharge or agricultural use, local legal requirements and actual water quality must be taken into account.

11. Prove environmental benefits with key figures

For a comprehensible evaluation, at least the following key figures should be recorded regularly:

  • Refill water per week or month,
  • Water consumption per kilogram of sales product,
  • Electricity consumption per kilogram of sales product,
  • amount of feed and fish growth,
  • plant yield and waste,
  • Amount of solids removed,
  • Frequency and amount of water changes,
  • Material and component failures.

Only this data enables a fair comparison with other production processes at the same location and under similar climatic conditions.

Practical check for water-saving operations

  • Refill line equipped with water meter
  • open water areas covered where appropriate
  • Lines and connections checked regularly for leaks
  • Filter cleaning documented
  • Rainwater use technically and hygienically tested
  • Fish stock, food quantity and plant area coordinated
  • Water values measured regularly
  • Pumps selected according to real operating point
  • Power consumption of important components is recorded
  • Nutrient and solid discharges controlled
  • Yield, water and energy evaluated together

Aquaponics can efficiently cycle water and connect nutrient flows between fish and crop production. However, a positive environmental impact only occurs if losses are measured, energy and feed are taken into account and the system is operated professionally over the long term.