Optimal pipe diameter irrigation system

There is no groundwater (property on the mountain) and at 1.5-2.0m rock is to be expected. Any deep construction can become harakiri because of that. We were lucky with the basement because the rising rock base starts there and our basement floor lies exactly on rock.

OK. Then only tap water remains. Take 1 inch. Just didn’t want you to regret later when the water bill comes.

Sure, thanks. We will use 2-3 more IBC containers for rainwater, but that's rather a drop in the ocean.

How big is your water meter? That is the reasonable diameter for your water pipe. A few things have already been mentioned. Cistern, well, etc. would be better. For 1000m2, quite a lot adds up. Hopefully practically laid out... Just as an example: lawn requires (worst case without natural rainfall) 20 liters / m2 / week. For 1000m2 that is 80m3 per month. Even with very economical watering you will need 10-20m3 per month. Don’t you have the possibility for a cistern or well? Another advantage would be that with a large pump (higher pressure and especially more flow) you can form larger irrigation circuits. Our garden area is estimated to be around 1000-1500m2 as well. I am planning for 20 circuits. 4 are spare. The difference is that I can realize circuits with over 6,000 l/h. The circuits also include drip and tree watering.

Yes, I am aware of the quantities. That's also why a "small" cistern is not an option. Cutting a large cistern into the rock is certainly not a cheap undertaking. A well is also out of the question due to the altitude. With 100-200m³ per year, you don't become poor and can draw clean(!) water for many years without technology, filters, or maintenance.

We still have nothing; the water connection will be installed in the next few weeks. According to the waterworks' offer, we will receive "PE pipe 32x3.0-H PN 16" and "KFR valve and bracket Q3 4" at the house connection.

The area is actually well-shaped, a free L-shape. Although 1000m² might have been an overestimate if you deduct outbuildings and other facilities in the final development.

For example, wells, cisterns, etc.?

They don’t interest either. The many cubic meters of water (therefore at least install the separate external water meter to save wastewater) will make you poor. Better to plan a few thousand euros for a well (with reasonable groundwater level maybe only 800€ including pump). Tap water on such a property is only economical if absolutely no other option exists.

Example: A simple Gardena Polo garden sprinkler (approx. 200 sqm lawn watered) consumes about 1.2 cubic meters of water per hour (at 4 bar pressure). You have more than 1,000 sqm = at least 5 units = at least 6 cubic meters per hour. What does water cost you? 2.00€/cbm (probably somewhat less + meter rent)? Plus flower beds, maybe a pool...
You can quickly calculate what tap water costs with that.

Sorry but absolute nonsense calculation.

Talk to your supplier to get a water meter with a large diameter. You need to optimize your system for flow. Otherwise, you will need many circuits/valves. Since well and cistern are not possible, you only have the water pipe left. Also, lay a KG pipe for the control lines through the wall right away. Then you can implement the control inside later.