# Node Types This table introduces the most commonly used Pywr node types:

Node Type	Icon	Brief Description
Input Node		Input nodes represent water inputs into the system.
Catchment Node		Catchment nodes are often used to represent river or other type of inflow into the system.
Proportional Input Node		Proportional input node is intended for a simple case of where fixed ratio of flow is required to be distributed to multiple downstream routes.
Link Node		Link node represents a link in the water system or other point of interest where a maximum or minimum flow constraint or an allocation priority are assigned.
River Node		River node is a node in the river network, which may have multiple upstream nodes (i.e. a confluence) but only one downstream node.
Delay Node		These delay flow for a given number of timesteps or days. This is used when flow propagation time cannot be ignored, for example because time-steps are relatively short.
Storage Node		Storage node is a general node that can store water (like dams or aquifers), which have a minimum and maximum volume restrictions.
Reservoir Node		Reservoir node is a type of storage node with additional functionality to represent evaporation and precipitation.
Output Node		Output nodes are locations where water leaves the system.
Loss Link Node		Loss link allows for the definition of a fixed proportional loss of flow that goes through this node.
Turbine Node		Turbine node can represent a turbine of a hydropower station. It calculates the flow required to generate a particular hydropower production target in each time step.

Pywr Node types can also be further sub-divided into 6 categories: [Water Input](https://water-strategy.gitbook.io/water-strategy/modeling-basics/node-types/water-input), [Water Transport](https://water-strategy.gitbook.io/water-strategy/modeling-basics/node-types/water-transport), [Water Storage](https://water-strategy.gitbook.io/water-strategy/modeling-basics/node-types/water-storage), [Water Output](https://water-strategy.gitbook.io/water-strategy/modeling-basics/node-types/water-output), [Hydropower](https://water-strategy.gitbook.io/water-strategy/modeling-basics/node-types/hydropower), and [Others](https://water-strategy.gitbook.io/water-strategy/modeling-basics/node-types/others). You can find more details about these groupings of nodes and nodes types in the sub-sections of the 'Node Types' section. ## More details An overview of nodes in Pywr can be found [here](https://pywr.github.io/pywr-docs/master/json.html#nodes.). The full list of built-in nodes in Pywr can be found [here](https://pywr.github.io/pywr-docs/master/api/pywr.nodes.html).