Rain water tanks

We have a 13k litre cistern -- feeds the toilets and washing machines and outside taps. The cistern did exist but with a hand pump when we got teh house - We had it plumbed in -- you will need a bypass - so if water is low you can use teh mains

Installation of a cistern isn't that difficult (We had similar sze tanks put in underground for teh sewage system.

Big hole - layer of fine gravel underneath for stability -- fill in (make sure you have manhole access) (consider teh siting so teat your run off pipes from teh roof can avoid going wher you may drive cars over if possible) We have a grundfoss pump that maintans teh pressure at 3 bar and automatically turn on if pressure is less -- ie when toilets flush or washing machine takes water.

You can find more details on teh net