Rain Water Collection
Using rain water to water CP's may not be completely necessary, but it's all I've ever used. I've heard of folks using well water, reverse osmosis water, even regular tap water may be good enough. It's just important to know what's in the water you're giving your plants. CP's don't like minerals, and chlorine isn't exactly a natural chemical they normally ingest either. I use a TDS meter to measure the "Total Dissolved Solids" in my water. These little devices can be purchased from Amazon for around $20. However, the safest route to go is collecting rain water if it is at all possible.
When I first started this adventure into this hobby of mine, I started with a 55 gallon barrel that I purchased from a seller on Facebook Marketplace. But as my plant collection grew, I found that 55 gallons didn't last very long. So, I upgraded my collection reservoir to a 275 gallon IBC tote (also purchased off FB Marketplace). Below are some pictures and directions on how I built it.
Cutting Hole in Tank and Installing Connection
To attach the plumbing to the water reservoir, I used a 2 inch PVC shower drain. You can pick this up a your local hardware store. They come complete with a rubber seal that works perfectly to keep the water in the tank. Once the drain connection is installed, all that is needed is a couple of elbows, a sanitary tee, and a few short lengths of pipe (all in 2 inch) .
As you can see in the pictures above, I arranged the 2" PVC fittings to essentially make an upside-down pee trap. This will allow all the rain water to flow into the collection tank as long as there is empty space at the top. Once the tank is completely full, the water will fill the pipe and begin flowing down the original downspout. At the top of the fittings, I used a 2" to 3" adapter to make a funnel. This setup works flawlessly for me, however it will overflow out the top of the pipe fittings during a torrential downpour, but not often enough to cause any damage or erosion. As an added feature, you can purchase a kitchen sink drain strainer to filter out any large debris before entering your collection tank.
Depending on the size of your roof and guttering layout, you may be very surprised to find out that your tank doesn't need a great deal of rain to fill up. I've had a completely empty tank fill to the brim after a short 15 minute summer shower. However, depending on the size of your plant collection and the water demands, it can become empty just as fast (or if you do like me and leave the water valve open and forget).
Another little tidbit of knowledge I've learned over the past few years it that the water in your tank can become stagnant over time. Just think of all the dirty contaminants that are on your roof (bird poop, pollen, and leaf decay to name a few) and eventually get washed down into your tank. It doesn't take long to notice an unpleasant smell to your water if it isn't occasionally drained and flushed out. So, if your water smells a little funky, just make sure that rain is in the forecast before doing a complete tank draining.