If you are going to fill a bucket and take it to where you want to use the water, dipping will often suffice. The storage tank can be mounted on a pad of gravel a few inches above ground level. This will reduce the amount of mud around the tank during rains and also keep the bottom of the tank relatively dry. The bucket is simply filled by dipping it through a top opening. The removable lid will need to fit tight to keep out mosquitoes and other critters. You will need to have a short tank with a large diameter so that you can reach the bottom of the tank as you empty it and so that you don’t injure your back while lifting out the bucket (a five-gallon bucket of water weighs about 42 pounds!). This type of installation is used in most countries where folks simply carry the water into the house or yard for use.
You do not need to put a hole in the side of the tank for a valve, pipe, or tube connection thus reducing the possibility for leaks.
It is least expensive and requires no electricity or wind power.
Construction materials can be very simple such as a trash can, adobe tank with a plastic liner, or a cob tank reinforced with branches, bamboo, or rebar and lined with plastic or stucco (see the tank section for more construction techniques).
There are no disadvantages that I can think of. It is perhaps a blessing to carry water. However, I have to wonder if the person that is carrying the water (for perhaps hours each day) is feeling fulfillment or dread. If it is dread, than we have identified another subject where we, as neighbors, might want to help, perhaps installing a windmill system. If the person is feeling fulfilled, trying to help them may be disruptive, invasive and perhaps a product of our ego.
A note about purification: Just because this method is low tech and at low pressure doesn’t mean you have to sacrifice water quality. Methods are provided in the purification section on making this water suitable for drinking and cooking.
5.2 Pressurization: Gravity
This is my favorite method of water delivery. If you are going to be filling buckets from an elevated tank, or using a hose to water plants, take a shower, or fill a toilet, gravity will work well.
Gravity offers the advantage of using free energy to produce a pressure, however, there is often a substantial cost for the structure to support the tank. The higher the tank is above a water outlet, such as a faucet or showerhead, the more pressure you will have to work with. Water pressure is measured in the US and a few other countries in pounds per square inch. Most city water is supplied to homes at somewhere between thirty and sixty pounds per square inch (psi) of pressure (as a comparison, your car tires are inflated to about 32 psi, your lungs can generated a little less than one psi while a nail gun operates at about 110 psi).
So, how high does a tank have to be to give reasonable water pressure? It depends on what you want to do with the water. For every foot of elevation you get about 0.43 psi of pressure (check out the tech spot below for how this is calculated).
Tech spot: The pressure supplied by water due to height is based on the density of water and the height from the top of the water to the outlet. The density of water at sea level (one atmosphere of pressure) and 60OF is 62.4 pounds per cubic foot (#/ft3). So for every foot of water height you get:
62.4 # 1 ft ft2 = 0.433 pounds per square inch (psi) per foot of water height. ft3 144 in2
If you mount a tank four feet off of the ground and the tank is full of water and the tank is four feet in diameter and you are using a hose laying on the ground connected to a spigot mounted near the bottom of the tank, the pressure at the end of the hose will be 8 feet times 0.433 psi/ft or 3.5 psi. If you are patient and you use a large diameter hose (5/8in or ¾ in), this is enough pressure to water your plants. With a 100-foot long ¾-inch hose you will get about 5 and a half gallons per minute when the tank is full. As the tank empties the pressure reduces and you will get about 4 gallons per minute just as the tank empties. If you have a two-story house and mount the tank eight feet off of the ground you will be surprised at the quality of pressure (about 6 psi). The water pressure in most municipal water supplies or well pump systems is between 20psi and 60psi so don’t expect the same water flow as you would get from such systems.
If a water tower in your neighborhood was designed to supply 60 psi of pressure to your house, it would need to be 60 # / 0.43 #/ft or 139.5 feet tall. Clearly your water-harvesting tank isn’t going to be that far off the ground so you can pretty much forget using gravity to give you a “strong” shower or pressurize a jet flush toilet. However, many of us use a lot more pressure than we need. If you are willing to change how you use water in your life, gravity can work quite well. Here are some examples:
Pressure needed to irrigate
It would be difficult to run a lawn sprinkler with anything less than about 20 psi of pressure. That would equate to a tank having to be about 47 feet high (20 / 0.43 = 46.5 ft). But it is easy to water plants with a pressure of about one and three-quarter psi (tank elevation of 4 feet) if you are clever about how you supply the water. Using a ¾-inch garden hose, closed off at the far end, and drilled with 3/16 inch holes about every foot would do nicely for a garden or flower bed. Simply turn the spigot on, set a timer, and move the hose after sufficient watering. My grandfather used a 20-foot, one-inch diameter galvanized pipe that he had drilled with 1/8 inch holes about every six inches apart, for his garden. He put a Tee in the middle for a hose connection so that he could carry the pipe easily, moving from row to row in his garden. He propped the Tee up with a piece of wood so that the water holes were always on top out of the mud. This also kept any dirt at the bottom of the pipe so it wouldn’t plug the holes. Every once in a while he would take the cap off the end of the pipe and let water flush out any dirt that accumulated in the pipe. I would encourage you to experiment with what works best for you. As you do, you will get closer to water, your plants, and have the best teacher in the world – nature.
Pressure needed to shower
Old English style showerheads were designed for hot water tanks mounted on the house roof or in the attic. The heads were big and they had many holes. This compensated for the low water pressure. You can get a nice shower flow with a tank mounted above your head if you use a showerhead that has larger than normal holes.
Pressure needed to flush a toilet
The jet toilets that are being sold today to reduce the water consumed per flush require a lot of water pressure to recharge the metal water tank that is hidden in the porcelain tank – about 40 psi. If you use a standard toilet, you only need enough water pressure to fill the tank (a source higher than the top of the tank). A rainwater harvesting storage tank five to ten feet above the toilet tank offers plenty of pressure as long as you are willing to have the toilet take longer to fill (you will also need to filter the water so the fill valve in the tank doesn’t plug). Tall buildings use water storage tanks placed on about every 21 floors. The tanks are at least 31 feet higher than the highest toilet and offer just over 13psi of pressure to flush a standard toilet. The height of the tank is such that the lowest floor gets about 80 psi of pressure. Any higher pressure would damage toilet and sink seals. You don’t need this much pressure; it’s just food for thought.
Heads up on gravity feed tanks
A bottom tank tap is convenient but can be prone to leaks if the tank is not made of steel, wood, plastic, or some form of cement. Lined tanks require special care in forming a good seal around the hole used for the tap. If you are going to use the water for drinking, I recommend two taps near the bottom of the tank. Make the first tap as close to the bottom of the tank as possible and make it large – at least four inches in diameter. Perhaps twice a year and when the water level is pretty low, flush your tank. Stir the tank as much as you can with a clean stick or broom and then immediately open this large bottom valve to let most of the sediment that collects on the bottom of the tank flush out. Keep stirring up the sediment until the tank is empty. The second tap should be about six to eight inches higher. Use this tap for every day use. It will allow the water to be drawn off above most of the sediment (see the chapter on tanks for more information on automatic tank blow down systems and tap locations).
A note about purification:
Again, just because this method is low tech and at low pressure doesn’t mean you have to sacrifice water quality. Methods are provided in the purification section on making this water suitable for drinking and cooking. However, your local city plumbing codes may make it difficult to get a permit to install a rainwater collection system for drinking water.