Water harvesting/storage

This bank holiday weather and the disappearance of spring here has got me thinking about water storage. I have a 200litre water butt collecting from the garage and am considering adding more butts to that setup. I am also thinking about adding gutters and a butt to the shed near the veg patch. 
From your experiences how much storage capacity do you need for your gardens, do you wish you had more? Thanks.

1. Lots, we have 14 butts most over 200 lt some collectors some storage and have been known to run out in a dry summer. We are on a meter and I hate paying for water if I don't have to.
2. Always

I have 3 interconnected ones on the garage; 2 on GH No1; 1 on GH No 2 and 1 on GH No3 - mostly blue barrel size.
Also a couple at the end of the garden collecting from various roofs and stores. That make 9 total.
Its usually enough but they're getting low at the moment.
I don't water the garden, apart from new plants, only the GHs.

We've got about 500L worth of storage and wish we had more, probably double would be OK. That's mostly for watering the greenhouse (10ft x 6ft) and outdoor containers. We ran out of water a few weeks ago and will likely run out again in summer if we have a prolonged dry, hot spell. I did water the raised beds this spring as the soil was getting very dry, most of the time I only water at planting. Part of the reason I prefer growing in the ground is the lower water requirement. In the greenhouse, the tomatoes and half of the peppers will be in the borders this year so hopefully they won't need watering so often.

One 1000 Litre IBC tank being fed from shed roof. Two barrels either side of greenhouse. Another IBC would probably see me self sufficient in water for plot as I had to fill IBC once last year from hosepipe.
We have no water at our allotments but one of the plot holders who lives close by gets his plot for nowt for  allowing us to use his hosepipe. His water isn't metered.

Got about 500L. collecting from house roof that fill up quickly when get any amount or rain so use these first. and 400L from a greenhouse. I don't use growbags now or pots except for starting plant off so everything in ground when warm enough. The house ones were getting low but all are pretty much full now.
It is very rare for all to empty (always keep 1/2 a butt for acid lovers) but occasionally have had to fill the 2 near the house. Not sure if I have needed to since I added the ones for the greenhouse.

I have 4 x 500l butts and can empty them in ten days in a hot spell during the summer, despite lots of mulch. But then one proper thunderstorm can fill them pretty quickly again!

Thanks everyone, so basically as much as I can collect and then some more would be the best bet.

I'm on a meter...I use the blue barrels size. I have 8. It's nowhere near enough. They were all empty a couple of weeks ago.

I never used to water the garden but over the last few years I have lost lots of plants due to lack of water....my new fruit trees, hedge, roses etc have been/ and will be watered until they are well and truly bedded in well as we have decided to not water them will cost us more if we have to replace.
I don't water annual veg/flowers etc, they get watered in well and then I try to use mulches where possible.

I have a 100lt barrel outside the greenhouse which I fill from the spicket, as generally it is only the greenhouse which requires regular watering,