How to provide enough water for my system

Water is not always available in the amount needed for your crop at the right time. Find out how to store enough water for your needs, whatever source of water you use. 

Which water sources to use 

The availability of water is highly dependent on the climatic and hydro-geographical conditions (the water that flows above and beneath the ground) of the region. Climatic conditions, like rainfall pattern and quantity, vary significantly within a year. 

Crop water demand depends on several factors:  

  • Specific crop type being grown  
  • Growing phase of the crop 
  • Growing method employed (soil, substrate, outdoor or protected) 
  • Irrigation system adopted (sub- or drip irrigation compared with overhead sprinkler application or hydroponic production)  

Irrigation water must be available in sufficient quantity to cover crop demand throughout the growing season, while taking into account any variation in supply. 

Water sources

Water can be taken from several sources; some growers may have easy access to multiple sources, while others experience difficulties getting sufficient water from just one. The majority of growers use only one water source. Mixing water sources can be useful if one of the water sources is of poorer quality. The water sources listed here are most relevant to a temperate climate. 

Water source 

Definition and use 

Fresh water 


Water extracted from underground aquifers. The quality of ground water can vary greatly between locations and is determined by the geology of the locality.  

Mains water 

Water provided through the regular network of potable water. Location affects the quality of mains water; for example, if it has a high calcium carbonate content. If high quality, it would be suitable for closed systems (recirculate all water and nutrient solution), otherwise more suited to open systems (water and nutrients not captured and reused). 


Also includes snow, sleet, or hail that falls or condenses on the ground or a surface (such as a greenhouse roof). Because of its low salt content, this water source would be suitable for both closed (recirculation) and open systems.  

Surface water 

Water from rivers, canals or ponds. The water from this source can often be polluted by a range of inorganic and organic materials; the quality of this water can, therefore, be lower than from other water sources, and would be best used in an open system. 

Recirculated water 

Drain water 

The excess nutrient solution provided to plants grown in artificial substrates such as rockwool, coir, peat, etc. Drain water does not pass through the greenhouse soil or substrate before collection. It can be recycled as a water source, so would be suitable for use in closed systems. 

Drainage water 

The excess nutrient solution provided to soil- and substrate-grown crops. This excess irrigation water passes through the greenhouse soil or substrate before it is collected through a below-ground pipe network. Although suitable for closed systems, it would need to be treated to remove excess salts, particles and any pathogens present. 

How much water storage do I need?

Water is not always available in the amount needed for your crop at the right time, even in the UK, which has relatively high rainfall. Rainwater is considered a high-quality source of water but, unfortunately, rainfall patterns rarely match up with the water demand of the crop. Whatever source of water you use, it is important to store enough for your needs:  

  • The first step is to calculate how much water you need to collect and store, and, therefore, the size of the storage facilities you need 
  • If possible, cover the water being stored 
  • Consider whether it is worth investing in below ground water storage to free up space on site 

Calculating storage requirements

Standard calculation tables specific to crops and regions are available. These tables were developed for horticultural crops, and give an overview of the storage needed to meet the water needs of a 1 ha greenhouse. More recently, models based on crop water consumption and long-term climate data (including rainfall, solar radiation, evapotranspiration, etc.) have been developed.

Above ground storage

Above ground, water silos are easy structures to put up, constructed from steel with a plastic lining inside. Ponds are relatively easy to create, being mainly excavation. If the water in the pond contains nitrogen or phosphorus, algae could become a problem. More involved is constructing a lined reservoir to store water, which prevents loss of water to the soil. Constructing a lined reservoir involves several steps, including a soil survey, calculating the size of the reservoir required, and excavation work. 

Useful links

See The Fertigation Bible for options for covering silos 

Below ground storage

Underground storage is useful to reduce evaporation, and removes issues with algae and contaminants such as bird droppings, leaves and other organic material. Underground concrete reservoirs are, in general, costly. They tend to be installed when a new glasshouse is built, to minimise disruption. There is also dynamic water storage underground, which expands and contracts depending on rainwater levels.