Water is present on the construction site

Drainage is nice and all, but when constant flooding has turned the soil into a swampy quagmire over decades, construction there tends to be unfavorable, and pile foundations and the like become necessary.

Drainage may also not work if an underground stream backs up during rain; you cannot and should not simply redirect it into the sewage system.

I don't want to paint the devil on the wall; in the end, it's simply surface water from neighboring properties that struggles to infiltrate the clayey-loamy topsoil and remains as puddles on the surface, while there may be optimal building ground beneath. Additional costs for a bit more excavation are at best not even worth mentioning.

With us, the water is also on the property because the soil is interspersed with clay layers. The soil survey showed no groundwater in the basement area. There was also no water in the excavation pit, and it was about 3 meters deep. But the old soil was not allowed to be refilled, but had to be replaced with compactable material, and that was not exactly cheap.

It may not be such a big deal, but building without a basement might be advantageous. Ask the neighbors if they have major problems with settlement cracks or similar. Or even a soil report. A bit of buffer for more foundation and earthworks must be planned.

I would not rely on a soil survey from the neighbors. We have a relatively large property (just under 2000 sqm) and have had several boreholes carried out, because groundwater came at 2m in the front section, we then built in the rear section.

If it is clay, yes, water often stands there. We also live on clay. We even have place names like Lehmberg. Infiltration is not possible. A rainwater drainage system is needed, which exists here and to which roofs and drains are connected. It drains into the lake. So no building basements! And little additional sealing. Better many plants or gravel paths instead of paving. Then you have it well under control. Nevertheless, we preferred to do without flush terrace doors and similar gimmicks because of heavy rain and snowmelt. K.