# Reservoir

> A reservoir is the tank that holds a system's water or nutrient solution, the place where pH, EC, temperature and oxygen are measured and adjusted.

- Canonical: https://genetixbay.com/knowledge/glossary/reservoir.html
- Also written: res, nutrient reservoir, nutrient tank, feed tank, rez, sump
- Glossary category: Systems and media · Evidence: Established
- Status: Draft: awaiting expert review · Updated: 2026-10-31
- Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary"

A reservoir is the container that stores the solution used to water or feed plants. In [recirculating systems](https://genetixbay.com/knowledge/glossary/recirculating-system.md), solution returns to it after passing the roots; in [drain-to-waste](https://genetixbay.com/knowledge/glossary/drain-to-waste.md) it is a fresh-mix tank. It is the control point for the system: [pH](https://genetixbay.com/knowledge/glossary/ph.md), [EC](https://genetixbay.com/knowledge/glossary/ec.md), temperature, dissolved oxygen and the microbial state of the solution are all managed here.

## In practice

Bigger is more stable: a large volume changes pH, EC and temperature more slowly. A common home guide is several litres of reservoir per plant, with recirculating systems sized so that a day's uptake is a small fraction of volume. Keep it lightproof to prevent algae, covered to keep debris and pests out, cool (about 18-21 °C, 64-70 °F) and well mixed. Log readings daily, top up as the level drops, and change or refresh it every one to two weeks in recirculating systems.

## Don't confuse with

- **Control bucket**: the mixing and adjustment bucket in [RDWC](https://genetixbay.com/knowledge/glossary/rdwc.md); part of the reservoir function.
- **Stock tank**: concentrate tank for injectors, not the working solution.

## Related terms

[Chiller](https://genetixbay.com/knowledge/glossary/chiller.md), [Dissolved oxygen](https://genetixbay.com/knowledge/glossary/dissolved-oxygen.md), [Recirculating system](https://genetixbay.com/knowledge/glossary/recirculating-system.md), [Beneficial-microbe reservoir](https://genetixbay.com/knowledge/glossary/beneficial-microbe-reservoir.md), [Sterile reservoir](https://genetixbay.com/knowledge/glossary/sterile-reservoir.md)

## Read more

- [pH drift in hydro: why reservoir pH rises (and sometimes falls)](https://genetixbay.com/knowledge/ph-ec/ph-drift-hydro.md)
- [Choosing your growing system: soil, coco, rockwool or hydro](https://genetixbay.com/knowledge/systems/choosing-a-system.md)

## Sources

1. Resh HM, 2022. Hydroponic Food Production, 8th ed. CRC Press. https://doi.org/10.1201/9781003133254