How to Build a Gravity Fed Water System

How to Build a Gravity Fed Water System

One of the most basic ways to build a running water system is the gravity-fed system. It consists of a cistern or holding tank at a higher elevation than the point of use. This allows gravity to do all the work of moving the water through the system eliminating the need for a water pump whether mechanical or electric. 

Contents

  • The Water Cistern or Holding Tank
  • Elevation
  • Filtering and Purifying
  • Construction
  • Types of Plumbing
  • Coupling and Flush Valve
  • Future Planning
  • Draining the system and system Shut-off

Water Cistern or Holding Tank

A cistern can be any size to suit your purpose. We use a 275-gallon IBC tote we purchased used for $30. It’s important to make sure whatever container you get is of food-grade quality.  You can usually purchase larger cisterns from farm supply stores or local farm coops. 

 If you use an IBC tote as we did you need to know that the connection points at the valve where you would thread plumbing fittings aren’t all the same. I wanted a tote that would be compatible with a standard 2” PVC fitting. The way I made sure I got the correctly threaded tote was I simply took a 2” fitting with me when I went to get the tote; Finding the tote I liked then threading on the 2” fitting.   

It’s also important to regularly look inside your cistern to see if it needs to be cleaned. If sunlight is allowed into the tank algae will grow and it will need to be cleaned periodically. Certain types of algae can be harmful to humans so don’t take this lightly. 

Elevation 

The cistern has to be elevated above the point of use. This can be done by constructing a tower, by putting the cistern on the roof or by placing the cistern on a hill at a higher elevation. 

The amount of pressure at the point of use will be determined mainly by the difference in elevation between the point of use and the cistern. the formula to calculate pressure is Pressure=.443*elevation in feet. This will come out to be 1 psi. For every 2’4” 

The advantages of a tower are you can build where it is most convenient for you and you can build it as tall as you want. The disadvantages are that you will have to find a way to pump the water into the cistern and the construction will get costly especially as it gets taller. 

Putting a cistern on the roof has the advantage of lower cost because you’re already going to build the structure where the cistern will be placed. Considerations in the construction of the roof will have to be made to accommodate the extra weight, but the cost savings will still be significant.

The disadvantage is the height will be predetermined by the height of the roof and you will still have to figure out how you’re going to pump water into the cistern. 

Placing the cistern on the land at higher elevation is the simplest solution because no tower or structure is needed to elevate the cistern and the amount of elevation is only limited by the topography of the land and it can be done in a way that allows water to be added to  the cistern fairly easily if the water is being hauled to the location.

The disadvantages are this set up will likely be the least convenient. The cistern is probably going to be a good distance from the point of use. And there will be some added cost because there will be a lot more plumbing pipe needed for this setup. The longer distance of plumbing pipe will also add some resistance to the water flow but it is minimal. 

Filtering & Purifying 

Whether you’re hauling water from a local source, pumping well water into the cistern or collecting rainwater you want to have a method for filtering and purifying your water. 

Bottleless Water Coolers

Treating your water is as simple as putting 1 tablespoon of bleach in your cistern for every 100-gallons. This just kills harmful bacteria so you’ll still need to filter the water to remove particles. 

Unless you’re getting your water from a municipal source you need to filter it to remove particles that may be harmful or at the very least can rack havoc on your plumbing fixtures. Modern fixtures are made with very small orifices which can easily be plugged and are sometimes impossible to get cleaned. So, take some time to come up with a plan to filter your water. 

A whole house filter is a good option because it filters everything coming into your cabin. These systems are fairly inexpensive and pretty simple to install. These filters are great at removing particles but aren’t designed to purify the water. I would recommend at least a 2 stage system using one filter to catch only large particles than a second filter to catch small particles. In the long run, this will make your filters last longer thus lowering your overall cost.

Click on the picture below to shop the many whole house filter system options available.

We’ve been using a Brita batch filter for our drinking and cooking water every day since 2014 with great results. The filter itself is inexpensive and the replacement filters are too. I would highly recommend Brita for a batch filtering system. 

Ideally, a bio-sand filter is the best option for an off-grid homestead because it will filter and purify your water at the same time in one system and once you’ve built it and seasoned it there are no other costs. No replacement filters to buy no Clorox or iodine etc. 

Construction 

Now that you have your cistern in place and you know how you’re going to filter and treat your water it’s time to hook it all up. This is pretty straight forward in that you connect all your plumbing pipes in your cabin to a mainline that connects to your cistern. There are some other considerations to make maintenance and repairs in the future a much simpler task. 

Types of plumbing pipe 

I used 1 ½” poly pipe to run from my cistern to the cabin and I used ¾” pex to run all the main lines for the water supply lines. Finally, I used ½” pex for all the individual water supply lines to the fixtures. This step down in size doesn’t increase water pressure, but it does increase water velocity which seems like better water pressure at the point of use. 

You can also use PVC, copper or galvanized steel pipe. I have found that the poly pipe is very durable and inexpensive and pex pipe is extremely efficient and easy to work with. Pex fittings are a little higher than PVC, but the amount of time saved in installation and repairs is quite substantial.  

Coupling and flush valve 

At the point where the mainline connects to the cistern, a coupler fitting will allow you to remove the cistern for cleaning without having to redo all the plumbing fittings to reconnect to the cistern. This will be just as useful if you ever want to upgrade your cistern. 

Click on the image below to shop coupler valves.

Directly after the coupling, you can install a T fitting with a shut-off valve going to the mainline and a shut-off valve on a line that dumps into a drain or into an irrigation tank. This can be used to clean or flush the cistern by closing the valve to the mainline and opening the valve to the flush line that dumps into a drain or irrigation tank. 

Future plans 

I would also install T fittings and plugs in places where you think a future plumbing project might happen. For example; when I ran our plumbing in our cabin the only fixture we had was a kitchen sink, but I made room in the plumbing lines with Ts and plugs for future additions. When I went back to add the bathtub, water heater and washer the plumbing lines were ready to go. 

Draining the system and system shut-off 

It is also handy to have a shut-off near the cabin to stop water flow from the cistern to the cabin. This allows for repairs and improvements while the cistern may be full of water. You will also want to have a drain valve at the lowest point in the system. This will allow you to drain the water from the entire system if needed or to just drain the water from the cabin while leaving the cistern full of water. 

Please leave any specific questions you may have in the comments. I read and respond to all of them and I use your comments to improve the content on this site.

For a very comprehensive look at rainwater catchment and gravity-fed systems I highly recommend the following book. Click on the picture below to check current price on Amazon.

Modern Potable Rainwater Harvesting shows how to design, build, and maintain a rainwater system that consistently and reliably provides potable water that is orders of magnitude cleaner than typical public municipal water. The book covers advanced oxidation processes, disinfection, biofilm control, filtration, plumbing, electronic controls, and water testing. Electronic schematics of essential control circuits are provided. Plumbing diagrams for both on-grid and off-grid systems are provided. Proper pump sizing for a given storage capacity is discussed. The book shows how to use a spreadsheet to properly size storage capacity based on actual rainfall data, collection area, and assumed daily usage rate.

To check out all the other books about off-grid living that I like and recommend go to my recommended books page.

https://offgridmaker.com/recommended-books/

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4 thoughts on “How to Build a Gravity Fed Water System

  1. Hi we have been running an off grid system for water in Spain for a few years. Also our power supply is solar. I installed 2 gravity tanks on our roof which we pump water up from a tank, all this works fine for taps toilets and boiler down stairs, but we use a water pump to push the water through the system when we need water to up stairs outlets. We have used 12 v seaflo pumps but unfortunately we have got through 3 pumps on our 4th inside 18 months. These pressture pumps are supposed to work when a tap turns on and off, but dont seem to work this way for long. I am no expert in water systems but fundamentally it’s fairly simple. What I am not sure about is whether our system needs any non return valves or a pressure tank to keep a steady flow when demanded. Or whether a different type of pump we have a seaflo 51 series in now only 3 months old and already having problems with pressure switch. Any ideas would be appreciated.

    1. It sounds like you could have a couple of issues going on.
      1) The design of your system is creating high back pressure which is putting too much strain on your pressure switch. In this case, you would want to install a backflow reducer https://amzn.to/3cGNOig. -or-
      2) This pump uses a micro switch to control (start and stop) the pump, they wired the pump motor directly to the switch and the switch is not great for inductive loads, It can be easily replaced https://amzn.to/38rFDDa. If you want it to stop having this issue, you can use a 40 AMP waterproof relay (Available on Amazon – not expensive https://amzn.to/2TKOZEE) and wire the switch to activate the relay and have the relay take to load of the pump motor – if you do this pump will last and work well for years without failure!

  2. It is a pleasure worth reading this article , which gives us suggestions on how to build a gravity fed water system.It is one of the best options to read from here in detail. I would go for this site even in future when needed. Great blog indeed, will visit again future to read more!!

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