Recycling shower water

When we are taking a shower, it consumes a lot of hot water. Water is used in an apartment house (some estimate) per day. Water is somewhat warm when it drains down to sewer. What if the water was poured directly to radiators just through some small filters. We could get water to radiators with less heating, when the water is already warm.

-> The same idea could sometime in the future be used also in dishwashers and washing machines.

The crucial question is: How dirty can the water in radiators be and how easily the radiators get blocked by the water?

Do sewers need hot water on the winter to stay unfrozen in some areas where the pipes aren’t so deep in the ground?

Buddy comments:

A typical water temperature is between 32-36C. In a part of radiators the fluid circulating isn’t water but glycol to prevent freezing. In addition there are two types of waste water: Light and heavy. The light water can be absorbed straight into nature, but the heavy must be gathered. The heavy water comes only from WC. Light waste water an be used in that system, if one cleans it well and the radiators are cleaned using pressure every now and then.

Another option is to use condenser, which would transfer the extra heat to central heating system with some efficiency rate. However most houses use district heating and it would hinder condensers function. Increasing the use of separate heating on the other hand would demand investments in heating and I don’t know if people are ready for that.

Tapani Heino: One could also use a heat pump, so the heat could be transferred straight from the sewer. Getting dirty is a challenge, what if there was only one straight pipe. Is there a point like that? The efficiency rate of heat pump is three, i.e. it takes only 1/3 of energy compared to how much it transfers.