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Pumps - Where and Why

by Doug Pushard

Pumps are a requirement for many rainwater harvesting systems, but what type of pump and where it should be located are questions that must be dealt with early in an installation. Most rainwater harvesting systems incorporate capture, conveyance, storage, filtration, and distribution components; and as part of the typical distribution system at least one pump will be needed.

In some small systems using either rainbarrels or a single above ground tank, no pump will be required: a hose will be all you will need. However, in almost all other systems a little more water pressure will be required. This does not always mean an electrical pump. For those interested in a workout, a little leg power can suffice (see Related Articles). However, the rest of us couch potatoes will prefer an electrical pump.

Normal household tap water pressure delivers about 10-20 GPM (gallons per minute) out of a faucet. This is more than enough pressure to run an irrigation system and the dishwasher or other appliance at the same time. Getting this type of pressure is where the pump comes into play.

In determining the proper pump requirements, several issues will need to be considered: location, type and size of pump. Cost, ease of installation, reliability and maintenance also matter.

The location of the pump is one of the first issues that should be thought through. It can be submerged in the tank or located outside the tank. Both options are common and can be made to work in almost all situations, although in some cases one or the other will work better.

Submersible pumps are safe and easy. The motor on a submersible pump is attached directly to the pump body, allowing the whole assembly to be submerged in the tank. They are designed and built with tight seals to prevent fluid leakage, which would cause short circuits.

These pumps are typically equipped with a large screen filter on the bottom of the pump housing. Water is pulled through this screen, pressurized and exits through a 1 ¼” – 1 ½” outlet on top of the pump housing. Wiring attached to the pump is generally 15-20’ long, and it is hard-wired into the pump on one end with the other end meant to be hard-wired into a safe power system. If you are going to install a pump yourself and are uncomfortable, inexperienced or unfamiliar with electricity, HIRE a professional to do the job (i.e., an Accredited Rainwater Professional www.arcsa.org, an electrician or plumber), as dealing with water and electricity can be a deadly combination.

Submersible pumps are oftentimes equipped with a float valve, which is highly recommended. A float valve shuts off the pump when the tank is nearly empty. The cost of this option is more than recouped if the tank ever runs dry and the pump burns out.

Submersible pumps are extremely reliable. A good, brand-name submersible pump may work for decades before requiring replacement or service. They are also less costly than above ground pumps to operate. They have the obvious advantage of working in the water, and they never lose prime. And since the pump is submerged there is little chance of accidents from an exposed motor and there is minimal noise when the pump is operating.

Submersible pumps should not be used in situations where freezing occurs inside the tank (e.g., above ground tanks in freezing cold states), as freezing will destroy the pump. Standard off-the-shelf submersible pumps range from 1/3 to 2 horsepower, are readily available at most plumbing outlets, large box stores, rainwater catchment suppliers, and generally run $200 - $425 for a good quality 1/2 hp pump. The more expensive pumps will typically have built-in controllers and integrated floats.

Non-submersible pumps (i.e., above ground pumps, that can either be free standing or buried in an irrigation-type box or other structure) are the other standard type of pump. These pumps are plumbed just like submersibles, with one end of the pump for drawing incoming water from the tank (usually 1 ¼ - 1 1/2” on the front of the pump housing) and one outgoing (usually 1 ¼ - 1 1/2” on the top of the pump housing).

An option for above ground pumps that is highly recommended for installations with below ground tanks is a self-priming pump. A pump running dry (i.e., without water) will burn out quickly and will most likely need to be replaced. The expense of a self-priming pump is more than offset if you burn out one pump.

These pumps are easy to maintain since they tend to be more accessible, are less expensive, and come in a wider variety of sizes and styles. These pumps are readily available at most plumbing and large box stores and generally run $125 - $400 for a 1/2 hp pump. The more expensive pumps will typically incorporate self priming as part of the pump.

 
Non–Submersible
Submersible
Cost
$125 - $400
$200 - $425
Ease of Installation
+
+++
Ease of Access
+++
+
Reliability
++
+++
Little to No Noise
+
+++
Life
++
+++

Size of the pump is another critical consideration. I highly recommend that you size your pump requirements, for current and future needs. Replacing a pump can be expensive. Seek a professional’s opinion on the correct size for your needs. Most installations will use between a 1/2 – 1 hp pump, depending on the use of the water and the amount required, distance to be transported, elevation (if any), and size of distribution piping.

A common mistake is to purchase a pump that is the wrong size or type of pump for the intended use (i.e., buying an inexpensive sump pump when a true submersible well or rainwater pump – is required). As the pump is often the second largest expense, after the tank, get a professional recommendation on size and type if you have any questions.

An option for smaller rainwater harvesting systems or rain barrels in need of a pump is a portable grey water pump. These pumps have been used for years by those dedicated to recycling as much indoor water as possible. Traditionally these pumps are used to remove water from washing machines, bathtubs and sinks for use in the garden. Both ends of the pump attach directly to a standard hose and are plugged into a GFIC equipped electrical outlet. One hose is put in the container to be drained and the other hose is placed where the water is to be used. They weigh only a few pounds and are meant to be carried to the task at hand and then disconnected and stored for later use. These pumps are a great way to start and can be found on the Internet by Googling XXX. They will not drive a standard irrigation system, but can deliver about XX GPM, which is more than enough to water a small yard with a hose or a small drip system.

Location is also a factor in deciding the type of pump to be used. Buried tanks can be plumbed with either above ground or submersible pumps, whereas above ground tanks tend to be plumbed with above ground pumps. Freezing is another factor which may dictate the use of an above ground pump as freezing a submersible pump will destroy the pump.

Pumps will burn out or require maintenance over time and are the one piece of a system that will probably have to be replaced at least once during a typical rainwater system’s life.

The purpose of the system (e.g., a potable water system versus an irrigation system) will affect what pump you choose. In most cases a small filter (200 mesh or 20 micron, depending on ultimate water use) is used with the pump. These keep small particles out of appliances, irrigation heads and other parts of the system to prolong the life of the components. Filtration is required by most plumbing and municipal codes for both inside non-potable water use or potable water use (see related stories on Filtration/Purification).

In determining what pump is best for your installation, consider location, type, size, cost, ease of installation, reliability and maintenance. In most cases there is no one perfect answer, so looking at the pros and cons of options will help you in designing a system that is easy to install, easy to maintain and supplies you a lifetime of rain. Please take care when working with a pump as you are dealing with the deadly combination of water and electricity. Hiring a professional is highly recommended and in fact required by most local building codes.

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