As there have been a few discussion on water storage .. thought I'd mention something that may be of interest.
I did a Selfbuild project for my house ... and one of the things that I thought our EU neighbours were way in front on, was storage of rainwater.
In Benelux countries all new buildings have to have an underground storage tank collecting all rainwater from the roof.
Or a shared unit for multi house developments.
This then provides untreated and 'free' water for garden, washing cars etc.
I took this to next level ... 75% of all water used in the house is actually used in flushing the toilet & in the washing machine.
So I built in a third water circuit ... i.e Hot Cold & recycled ... so all cisterns, washing machine, outside taps etc. off third circuit.
Underground I have a 5,000 gallon storage tank ... all gutter pipes go to this, and there is basic filtering at each gulley, and a coarse leaf filter in tank.
When tank is full water overflows into normal surface water drain.
It has a built in high pressure high volume pump, and a float arrangement so that water is always 'pumped' from about 4" below surface.
On checking in annually water is always clean, fresh .. maybe as it's totally dark, environment no algae growth.
The house side has a control unit ... that keeps a small container of water pressurised, so if you open a tap .. you get instant mains pressure .. then pump kicks in.
Should tank get low, if it gets to less than 10% it will auto top up from mains so no need to change any plumbing.
If anything should fail, there is a manual lever to switch 3rd circuit to mains water.
The plus is you get untreated water for your washing / car/ garden etc. ... no chlorine.
It's yours so not affected by hosepipe bans.
Once installed - it's almost free (small cost on pump)
I am on a meter so drastically reduced water charges ...... and as much water as I want for garden.
This is such a no-brainer solution that UK should force this to be required on all new builds.