How long can I store water in a rainwater cistern?

our irrigation system pumps about 1200 liters of water into the garden almost daily.

Really? That is about 216 m3 of water just in the summer half-year, and that without a cistern? Either you have different water prices or a fat wallet.

Hi,

Advice 1: Forget the nonsense about the cistern, it does neither good for the environment nor for the wallet.
Advice 2: If you really want to do it, take the large 8000 l cistern.

Best regards,

Andreas

I think that argument is such nonsense. Of course it makes a difference whether I use rainwater from the cistern or drinking water. On average, you consume 15-20L/sqm per week (summer months), so with 300sqm garden that's 6000L of water per week. The filters are planned from the beginning and don't cost a fortune. Please also consider the wastewater and drinking water fees for this amount of water over the years.

Regarding the environment: Drinking water is processed energetically, which is not really beneficial for the environment. So why not use the opportunity and simply use the rainwater?
Just think long term!

on average, 15-20L/sqm per week is consumed (summer months), so for a 300sqm garden it's 6000L of water per week.

With all due respect, these values cannot be applied universally. We have just under 600m2 of garden, planted with grass, trees, and hedges. Everything is only 2 years old, and except for new plantings or really long dry periods, almost nothing is watered.

According to your rough calculation, I could buy the waterworks otherwise.

it will probably be 620 l /sqm per year, that is 62,000 l on the roof per year.

You are of course right, stupid comma!

The values have been googled, we do not yet have experiential data

Hi,

Really? That’s about 216 m3 of water just for the summer half-year, and that without a cistern? Either you have different water prices or a fat wallet.

It’s not quite that much. I started the irrigation at the end of April or beginning of May and have since used about 55-60 m3 of water in the garden. Over the summer, about 120-150 m3 will probably be reached in total. Water costs 1.8 €/m3 here and, of course, we have a separate garden water meter, so no sewage fees are charged for it. That means max. 250-300 € per year.

And what does a cistern with pump and everything else fully installed cost? Have you done the math?

The problem with a cistern is simply that it doesn’t store enough water in normal sizes to bridge longer dry spells. The neighbors with cisterns have exactly that problem here as well. Of course it’s full in spring, but from early summer it’s mostly empty and then tap water is used for watering anyway.

I’ve attached the rainfall amounts for our area.
Maybe that makes the problem clearer. Here it sometimes rains 40 mm (which with our roof area is about 4000 liters, enough for 3-4 days) but then we often have a “drought” for 2 weeks. That means the cistern is enough for 4 days and then 10 days of watering with tap water.
In other words, even a cistern would at best reduce our garden’s water consumption by 40%.
So a saving of at best 100 € per year. And for that to build a cistern costing 2-5k€ in the garden?

Anyone can do it if they want, but I wouldn’t.

Best regards,

Andreas