I can't see the point of changing all the pipe sizes unless there is a problem with flow, such as to the shower or bath. Oversizing all the other pipes and fittings only increases the opportunity to waste water and waste heat.
I have just fitted free low flow aerators to the basin taps, they may save a few pence off the water bill https://watersavingdevices.thameswater.co.uk/
Looking to add a pump to the shower as flow isn't that great. Also fluid dynamics ;) looking to add filters to the drinking water and that will restrict the flow.
I can't see the point of changing all the pipe sizes unless there is a problem with flow, such as to the shower or bath. Oversizing all the other pipes and fittings only increases the opportunity to waste water and waste heat.
I have just fitted free low flow aerators to the basin taps, they may save a few pence off the water bill https://watersavingdevices.thameswater.co.uk/