# Calculating domestic demand within the model

Reducing Non-Revenue Water losses (NRW) is a possibe intervention. A large part of NRW losses is a result of leakage. Retrofitting water mains as well as pressure control could reduce these losses. Gaborone currently experiences ~29% NRW while other areas have as much as 37-59 % NRW losses.

Each demand node's demand is defined by a Pywr parameter which calculates the demand of each demand node. The parameter is placed in the max_flow attribute on each demand node.

For example the demand for the Gaborone Demand Centre is shown below (**Gaborone DC max_flow**):

The parameters are defined in the Parameters tab:

In the Parameters tab the** Gaborone DC max_flow **is shon to be an Aggregated parameter which uses multiplication to combine four additional parameters together

Each domestic water demand in the Botswana national water resources model is calculated as a product of four paramter values. For Gaborone these are:

**"Gaborone DC baseline":**Baseline water demand in 2020**"domestic_scn factor":**A future uplift factor quantified by an increase in the population and Per Capita Consumption"

**Gaborone DC NRW factor":**Non-revenue water factor**"Gaborone&Bokaa saving factor":**Demand reductions resulting from water use restrictions imposed due to low reservoir levels (usually no demand reductions are implemented and this value is 1.0)

These factors combine to produce the final water water demand for each domestic demand node.

Each of these four parameters is also defined in the Parameters list.

For example, Gaborone's NRW factor is **Gaborone DC NRW factor** and can be seen in the Parameter tab as:

The value is 1.4015. This value is applied to the amount of water delivered to the demand after NRW losses (i.e. the net water delivered to a demand). A value of 1.4015 represents a NRW loss factor of 28.6% when applied to the gross amount of water put into the distribution system before losses.

The **Gaborone DC baseline **represents the 2020 demand and is 0.06968 Mm3/day.

The **domestic_scn factor **represents the increase in demand from 2020 and in this case is 3.5 representing 350%.

When multiplying all the values together the Gaborone demand in this scenario is 0.3418 Mm3/day.

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