The house is connected to mains water. We had it completely replumbed (replacing old iron pipes with new copper) when we first bought it.
When we were installing cisterns for the toilets we put in the most efficient we could get at the time. For the renovation of the original part of the house that was 12/6 litre dual-flush (now replaced by a 4.5/3 unit). For the extension it was 6/3 litre dual flush.
We have also fitted flow-reducing valves in both showers to take them down to a maximum of 9 litres per minute (lpm).
More recently, we decided to fit rainwater tanks to enable us to keep our garden alive during the ongoing drought/permanent climate change. We decided to pipe all of the gutters to one corner of the house and run them into a connected series of three 25000 litre tanks. These are connected to a pump to provide mains pressure water to feed the toilet cisterns and the washing machine. The pump also has a RainBank attachment so that if the tanks run dry it switches automatically to mains water. Because the gas meter is located behind the tanks, we had to leave a gap between the tanks and the fence to allow the meter-reader to gain access to read it.
We also have a smaller 600 litre tank fed by the tool shed. We use this to provide water to the chooks, and also to water some of the fruit and nut trees.
With the benefit of hindsight, we made some mistakes with the rainwater system:
In general, it would have been good to fit more capacity - it's a very nice feeling having lots of capacity, and very annoying to hear water running down the drain once the tanks are full!
We are thinking how best/most cost-effectively to add more capacity. Probably fitting another tank would be the cheapest option, although we will have to build up the ground to the same level as the others to allow all the tanks to work as one system.