Over the summer, we had a mechanical engineering intern named Chanon helping out on an experimental project.

The problem is that while rain water is mostly clean, the roof it hits is often not. In addition to the dust and other pollution that collects between rains, there is also feces from birds, lizards, and other creatures. But most of this stuff washes off in the first rains, so the rain water coming off of the roof later is much cleaner. (I have read numbers of up to 90% reduction in E. coli and other nasties.)

Since we have a rain gutter on BaanMae, it is easy to collect the rain. But the idea here is to build a contraption to gather up the first rains and divert them away from the normal water storage cisterns. This way, the cisterns contain water that is less likely to cause illness if it is used to water gardens, etc.

This contraption is called a first flush rain diverter.

So Chanon spent a few months on this and I think he did an excellent job.

Here is a picture of the diverter filling up after a rain in mid July:

It is made mostly out of PVC pipe. The greenish-brown section down below is actually a clear acrylic tube where you can see the water. In this case, you can see how murky the water coming off the roof actually is. The idea is that the clear chamber fills up with about 8 liters of water. Once it is full, the inlet to the chamber seals up and the water is diverted to the side to come out freely and flow down to the cistern below.

Here are a few pictures from the other side a few days later:

Inside, you can see the blue 3D printed ball floating on the water. This ball floats up as the chamber fills in and eventual fits snugly into a concave 3D printed piece at the top to provide a simple seal to the “dirty water chamber”.

If you zoom in, you can see that there is a red valve at the very bottom allowing us to empty out the diverter. I’ve attached a clear plastic tube to this valve and I’ve been experimenting with adjusting the valve so that the water just drips out slowly (over the course of about 5 or 6 hours). This way, it automatically empties itself into the dirt underneath the house before the next rains come without any need for me to do anything. (And if rains come within about 6 hours, the roof probably hasn’t had time to get dirty again anyway.)

You can also see how the water on these later pictures is much clearer than the earlier rain. Since it was raining almost every day at this point, the first picture above contains some of the dirtiest water because it was the first rain in a while. But the later ones represent less than one day’s buildup of dust and crud.

Pretty cool design. Good job Chanon!

And if you agree that the blue PVC doesn’t fit with the aesthetic of the house, we tried painting it “wood colored”. Not perfect, but certainly better. 😉

We’ll be adding a “water chain” to guide the water down the spout to the cistern below.