On average there is 30% drain/drainage water. Clean water is also added to the water cycle, mainly rainwater from the basin. This makes it the easiest to put the drain water collected into the rainwater basin. "But adding drain water to the rainwater supply isn't a good idea due to the biological balance. The fertilisers that you are bringing into the basin by doing this, cause plants to grow. Algae in particular grow well in this," says Bakker. "It also causes an uncontrollable situation. In a low rainwater level there will be a higher concentration of drain water and when there is a lot of rain the opposite will be the case."
Adding ditch water to the basin also causes an algae explosion. Partially because the rainwater basin has a fragile ecosystem. The surface water, which has more bacteria, viruses and diseases in it, disrupts this balance. And this water can be food for plants. Bakker: "Everything you don't want pollution wise is in surface water. So don't add ditch water to the rainwater, keep them separate for irrigation. Do this in the spring and use clean rainwater in the summer."
When mixing other water is done wrong, it has consequences. This is why the various flavours of water, such as rainwater, pipe water and osmosis water are buffered in a separate silo. This is also done with separated collection of dirty and clean drain water. At new companies condensation water (water that the plant has condensed itself) is even collected in a separate silo and used first and given in controlled doses with the feeding water.
Don't turn off the filter
During the growing season the rainwater supply often does run out, sometimes even in spring. Then all kinds of water are pumped up and added to the rainwater to supplement it, which means a lot of dirt (algae or muck) end up in the basin. This clogs up the filter. Bakker: "Growers then sometimes ask whether they can take the filter out. We say: don't! But sometimes you can't help it, you have to water the plants or they'll wilt." Prevention is better than remedying.