How much rainwater to store

Hello All,

I am planning to convert my garden to a more permaculture styled one where I can grow some food and get my fingers dirty to relax. Can anyone give me some pointers on how much volume of water I should try to store ? I am trying to research this but I have thus far failed to punch in the correct words into google As far as I can tell from various youtube movies people have man height round tanks which would mean about 2000-3000 liters ?

I live in the Netherlands which is a temperate climate and under influence of the north sea. This year we had a fairly wet summer (streams in the forest were full) and pretty dry fall (streams were a lot lower and artificial rapids stopped running).

Backyard drawing including coordinates:

How much rainfall have you and how big is the roof you will be collecting from ?

David Livingston wrote:How much rainfall have you and how big is the roof you will be collecting from ?

Thank you for answering, here are the details:

Rainfall (12 year average):
Jan 70mm
Feb 61mm
Mar 51mm
Apr 38mm
May 75mm
Jun 63mm
Jul 94mm
Aug 93mm
Sep 51mm
Oct 67mm
Nov 67mm
Dec 82mm

The roof I potentially could collect from if I changed the gutters and diverted water towards tanks in the backyard would be:
- 8 m^2 flat roof
- 10 m^2 side roof (angled about 40 degrees)
- 37 m^2 main roof (angled about 40 degrees)

There are many factors that go into how much water you should store such as 1. How much water will you need, 2. When will you need it, 3. How does the rain usually fall when you need water (1 big thunderstorm per month, or multiple rainy days), 4. How long can the things you are growing go without water, and 5. How willing are you to use city/well water...

Here is a video that addresses some of these issues.

Storage is usually monthly demand x the number of dry months you can expect.  If I need 3000 gallons a month and we typically get 4 months of no rain, then I need 12,ooo gallon capacity  to cover me.

Your rain seems pretty consistent based on the averages. I'd suggeat getting a tank and add more as needed. If you currentry get a water bill, you can use that as a baseline.  You'll have to make assumptions, like what % goes to garden vs bathing. Not sure Google can give that data. It's so different from home to home.

Thanks everyone,

It seems that it comes down to "It depends". I did some more research and it seems that on average I should have >1mm of rain every 2.5 days. What I will do is create the water soaking systems first and redirect the downspouts into them, I will add the storage later if need be.

Christian van der Stap wrote:Thanks everyone,

It seems that it comes down to "It depends". I did some more research and it seems that on average I should have >1mm of rain every 2.5 days. What I will do is create the water soaking systems first and redirect the downspouts into them, I will add the storage later if need be.

I'd urge you to put at least a rain barrel in between your gutter and your soaking systems.  When it's raining, you don't need to add more water at the exact same time - you probably need it a couple of days later.  I'd be concerned about erosion or damage to young plants with a simultaneous double watering.  So I'd recommend blocking gutter runoff from the garden into storage, when it's full redirecting it *away* from the garden, and releasing it to the garden on dry days.

If my assumption is wrong, then you could just unblock the connection.  A rain barrel runs about $100 (some cities will provide subsidies, at least in the US) which is annoying if unneeded but probably small on the scale of a "water soaking system".

Best regards!

Morfydd St. Clair wrote:
I'd urge you to put at least a rain barrel in between your gutter and your soaking systems.  When it's raining, you don't need to add more water at the exact same time - you probably need it a couple of days later.  I'd be concerned about erosion or damage to young plants with a simultaneous double watering.  So I'd recommend blocking gutter runoff from the garden into storage, when it's full redirecting it *away* from the garden, and releasing it to the garden on dry days.

If my assumption is wrong, then you could just unblock the connection.  A rain barrel runs about $100 (some cities will provide subsidies, at least in the US) which is annoying if unneeded but probably small on the scale of a "water soaking system".

Best regards!

Thanks for inspiring me to rethink this. I managed to find a spot for an IBC to store water, I just need to add a downspout which runs from the main roof gutter to the IBC passing the flat roof. Here is the plan I have for doing to water works in the garden, the ditches will likely get a drainage pipe in them to spread the water quicker.

Current:


Planned:


I still need to figure out if I will need a first flush diverter or not, it seems that I can get away with not having one as I will only use the water for irrigation.

I would recommend a first flush diverter- they push the need to drain and clean a clogged IBC tote outlet back substantially, and can be quite simple and cheap.

like this one: pipe and bucket simple machine:

Cody DeBaun wrote:I would recommend a first flush diverter- they push the need to drain and clean a clogged IBC tote outlet back substantially, and can be quite simple and cheap.

like this one: pipe and bucket simple machine:

That is a nice design, however I would use a floating ball type because then the pipe can stay closed. When the IBC is full, the water will back fill to the gutter and flow towards the next pipe down to the sewers.