Rain-Fed Watering System

The amount of rain that falls is incredible and I admit that as I watch it run off of our property after a storm, I know I’m not making good use of that resource.  Ideally, we could leave our livestock to drink from streams on the property, but when our neighbors are spraying who knows what and who knows when, we can’t be sure what those streams contain.  We can, instead, equip our barns with rain-fed watering systems and avoid the trouble while also capturing the fresh water God provides.

1.  Calculate the amount of water that a shower provides is pretty easy.  

  • Measure the size of your barn roof–in inches.  If you barn was 30′ x 30′ (length x width), that would be 360″ x 360″, giving your roof an area of 129,600 sq. in..
  • If you had 1″ of rain, that would make the volume of water on the roof 129,600 cu. in. (area x depth)
  • There are 231 cu. in per gallon, so dividing the volume of water by 231 will give us the volume in gallons.  129,600 cu. in. / 231 in/gal = 561 gals.

1 inch of water on a 30′ x 30′ barn is 561 gallons!

2.  Calculate average rainfall.

The size of your tank will be determined not by how large a tank you can afford, but how much rainfall your farm receives.  Here in central NC, we receive 45-50 inches of rain per year, which is just under 1″ per week.  Thus, on a 30 ‘ x 30’ barn we would receive about 561 gallons per week.  That’s important to know.

3.  Determine how much water is needed.

It makes no sense to buy the biggest tank you can afford.  Your tank size will be determined by how much water you need and how much rainfall you get.  A dairy cow can consume 20 gals of water per day, which would be 140 gallons per week.  Rain from a 30′ x 30′ barn in our area could supply 4 dairy cows for a week.  A large rainfall will overflow a small tank, and a larger tank will allow you to capture more of a large rainfall.  Therefore, a 500 gal tank (about $420 would stay pretty full on a 30′ x 30′ barn.

The water tank is going to need to be cleaned, so you don’t want it full all the time.  You want to be able to shut off water flowing into it, so your animals can empty it and make cleaning easy.  It will need to be washed and scrubbed out and sanitized, along with the pipes that feed it and are fed by it.

4.  Purchase your water tank.

water tankThis is the expensive part of the  job, but it separates your barn operation from your well water supply.  That’s a big deal and worth the money.

We can compare three tanks 500 gal ($430), 1000 gal ($600) and 1500 gal ($800)  available from Tractor Supply here.  Notice that you save money when you buy a larger tank, so going small is not necessarily a good idea.  If you have a large barn with lots of animals, you can use more than one tank, but the largest tanks you could get would be the most affordable.

5.  Locating your tank

Ideally, your water tanks will be higher than your water supply outlets and shaded to keep water cool.

You can’t go ghetto here and think that sticking a plastic water tank on the ground will work well for you.  People who don’t spend money also don’t make any.  You’ll need to set your tank on a cement slab or metal stand to allow for cleaning, etc..  Your water tank would need to have some hardware installed including a flush valve in the bottom for cleaning, and an outlet a few inches from the bottom for your water supply.  Water going into the tank needs to be filtered to keep out leaves and debris from the gutters.


It’s not difficult to establish a rain-fed barn.  Some calculations are required and an investment made, but this arrangement allows us to put barns anywhere on our farms with no worry about water supply.



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One Response to Rain-Fed Watering System

  1. Devin Rose says:

    Great post. We are planning on catching the rainwater from our house roof, garage roof, and barn roof and using two, 2500 gallon tanks for storage. We will then use this water for our home usage via pump, pressure tank, and filters.

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