The topic of rain barrels came up in the comments
over at Aunt B's yesterday, and it got me started thinking about my own grandiose rain barrel plans again. Before we go down this road I'm just going to remind everyone that I'm an engineer, and water is my specialty area. So things can and will get out of hand with this post. I'm also used to working on a grander scale than my 1/5 acre back yard and with a higher budget. Most of my plans will just be me brainstorming and probably aren't feasible unless you have a much larger operation than the average suburb dweller.
If you aren't familiar with the concept, a rain barrel is a storage device used to collect rainfall runoff, generally from the roof of a building, and store it for later use. Just to illustrate the concept, let's assume a 1000 square foot house with a roof that peaks in the middle and down spouts at each of the four corners. Say that you get a one inch rainfall over the course of a day (a respectable storm in middle TN, but not that unlikely). You end up with about 83 cubic feet of water. Enough water to fill up my 10 ft x 10 ft guest bedroom eight feet deep with water. That translates to 623 gallons of water for one inch of rainfall. Consider that the average annual rainfall for Nashville is about 47 inches, and the monthly average varies from 2-4 inches. That's a lot of water that doesn't get used. (This is a great source for historic rainfall monthly and annual averages if you want to check other cities/regions.) Just position the rain barrels under your gutter down spouts and get to saving money on your water bill.
There's a lot of variability in rain barrels use. I was doing some internet research to figure out how to build one to water my yard, and I ran across quite a few ways of caputuring rainwater and using it. It's probably not a good idea to drink rainwater without purifying it, but you can use it for just about anything else. Most common by far is watering yard/garden/landscaping but I ran across one 'how-to' for using rainwater to flush your toilets. The main limitations are the size of your roof and how much water pressure you need.
There's also a lot of variability in the barrels themselves. If you're feeling like a big spender you can get some nice decorative ones all over the internet. My personal plan was to build them myself. Nashville's Department of Water Services has
a good primer on how to build your own. A key cost saving tip... get some of the large 55 gallon barrels used by bottling companies like Coca Cola. I haven't investigated this for myself, but rumor has it that you can usually get used ones for free if you call the local bottler. They aren't pretty, but the price is right.
You do have to consider whether rain barrels are illegal in your area. I'm not going to go into the reasons why, but in some of the more arid climates local governments have outlawed rain barrel use.
Elevation is the enemy of rain barrels. All the water pressure you get is going to be from the height of the water. You need to have downhill flow in order to get the water from the barrel to the place it's needed. It's also a general rule of thumb that the longer the hose the lower the pressure at the end of the hose. If your garden is a long way from the rain barrels, or up a hill, then you're probably out of luck but if the distance and elevation changes are small, then you might be able to get around it. The solution is to build elevation into your system. If you put your rain barrel on a pedestal you can get a little extra pressure. You have to be careful how high you put it though because water is heavy and you really don't want your barrel falling on the dog.
So let's assume you have a three foot tall barrel and you put it on a three foot tall pedestal. That means when the barrel is full you have six feet of pressure in your system. So if your garden is five feet higher than the ground where your barrel is, then the first foot of water in the barrel can be used in the garden. If your garden is three feet higher then you should be able to empty the barrel into the garden.
If your garden is too far uphill, all isn't lost. You can pressurize your system using the same methods that drinkable water is delivered to your house. Put in a pump. But, this is when you start having to spend money when the whole point of the rain barrel is to save you money. If your garden is too far uphill for the pedestal to work, you're probably better off just hooking up the hose to the back yard spigot and paying the water company.
I'm getting all stary eyed now that I'm to the part where I talk about my own plans for a rain barrel system. Notice I said 'system'? That's where it gets bad that I'm an engineer. My lot slopes up from the front to the back, with my house about half way up. So rain barrels for the front of the house are no problem. The barrels will be at the top of the hill and I can water my front yard with gravity flow. Unfortunately the garden is going to be in the back yard. The area I have picked out is about halfway up the slope so I need to build a little elevation into my barrels.
My ideal solution requires a pump. My rain barrels would be at the corners of the house and both would be hooked up to a single pump. The pump would lead to a small reservoir consisting of extra barrels along the back fence. The reservoir barrels would be connected together and a soaker hose would be hooked to the outlet. So whenever my barrels at the house get full I would just turn on the pump for a couple of minutes and all the water would go up into the reservoir barrels to be saved until I needed it. Then I just turn the valve on the soaker hose and let gravity do the work. This way I don't use the pump very much, but still get plenty of water pressure. Pump it to the top and let gravity do the rest. It's a variation on the same principle used with all those water towers you see built so high in the air.
Unfortunately, that system probably isn't very feasible, what with a pump and all that piping to be laid in the back yard. So I'll probably just let the water company provide the water pressure.
