ᐅ Cistern overflow too low for natural drainage overflow

Hello,

After searching online for a long time, I believe I have not yet looked for the right solution.

We are currently building a new house and plan to use a rainwater cistern to water the garden later. However, there are a few conditions to consider.

1. Excess rainwater must not flow into the sewage system.
2. Excess rainwater must be discharged into the street.
3. The cistern will be located below street level.

This means we need a system to pump the overflowing water up to the higher street level.

I have already looked at various pumping systems. However, from an ecological perspective, the cistern does not make much sense if the benefit is offset by using a pump. Also, so far, I have mostly seen submersible pumps, which would not remove debris from the surface water of the cistern.

Hoping that we are not the first to want to use a cistern under these conditions, I look forward to any valuable new suggestions.

Best regards,
FlorianBaaske

Normally, it is not allowed or recommended to discharge surface water from a private property onto a public street. If everyone does this, the drainage system designed for the street will no longer function properly!

Point 1 is correct.
I see point 2 differently.
Point 3 will "almost" always be the case that a cistern is located below street level.

Interesting topic, I worked on something similar today.

We are not allowed to let the rainwater infiltrate at a single point and we also have no connection to a pipe for this. We are required to collect the water in a cistern and let it infiltrate through soakaways. This might also be an option for you.

Is there no way to install the cistern so that the overflow is above ground level?
Otherwise, I only see a pump as a solution or an infiltration system on the property.
You already have a pump to extract water anyway. I could imagine using a sensor and a multi-way valve. When the water level exceeds the preset limit, the valve automatically switches, the pump starts, and lowers the water level.
Are you really allowed to drain into public land or the sewer system?
That would be great if it’s permitted. In many areas, there is too little water in the sewer system, and it has to be flushed with fresh water.

There are also shallow tanks that are not installed as deep, allowing for a relatively high outlet. The question with the pump is whether it can actually manage to remove the water during a heavy downpour.

What kind of surface areas are we talking about that will drain into the cistern? How large should it be? If you want an automatic irrigation system, you will need a pump with sufficient volume and pressure anyway. A pump with, for example, 6 m³/h (about 158 gallons per hour) can move enough water... large height differences are probably not manageable.