Tag Archives: RainBank Tech Facts

Is Acid Rain a Concern in Rainwater Collection?

raindrop stock photoWhy worry about acid rain? pH level is a quantitative measure of hydrogen ions with a level of 7 being neutral. Anything less than 7 is considered acidic, with anything above 7 considered alkaline. In the Pacific Northwest pH of our rainwater is typically 5.5.

Drinking acidic rainwater is not normally a health concern, however lower pH levels can cause blue/green staining in sinks and tubs, and sometimes in severe cases, may cause leaching and damage to copper plumbing. Simple pH testing strips can indicate the pH levels in collected rainwater. Generally, the smallest amount of buffering can adjust levels to a nominal 7.0 , or neutral. Adding 4 ounces of baking soda in solution to every 1,000 gallons of stored rainwater is an effective method of adjusting pH. It is recommended to start with the minimal amount, then test again and increase if necessary.

Neutralizing filters typically contain calcium carbonate, which dissolves as it interacts with untreated water, increasing pH values to appropriate range through addition of neutralizing materials, increasing to 6.5 pH to 8.0 pH although spikes in hardness may incur. Chemical pumps can inject calcite into the water flow after filtration and are effective if placed upstream of the pressure tank or day tank.

It is advised that testing pH levels at the storage site, as well as at the tap be conducted before adjusting. Variables such as temperature and materials used in the water system itself can have effects on pH levels, so it is good to know where your baseline is. Sampling can be done by a lab for accuracy if required.

The key is to know, maintain, and service your rainwater collection system for best results.

Rain Drop Stock Photo courtesy of samuiblue / www.freedigitalphotos.net

When are Diaphragm Pumps Used in a Rainwater Collection System?

Diaphragm PumpAlthough centrifugal pumps are the most common type of pump used in rainwater collection systems for both sump pumps and pressure pumps, diaphragm pumps could be used in some applications.

The diaphragm pump, or positive displacement pump, uses a flexible membrane that separates the pump housing into two separate chambers. The membrane is pushed or pulled by mechanical means to enlarge or collapse a chamber, forcing the fluid to discharge. Non return valves are used on both sides of the diaphragm to prevent back flow. Electrical, mechanical, or manual can be the power supply for a diaphragm pump. A hand pump is a piston type diaphragm pump and used throughout the world, where there is no source of a power supply.

Air, chemical, and liquid can be pumped with a diaphragm pump with high efficiency. However, because of the reciprocating mechanical action or “pulsating” that occurs, a diaphragm pump would not be suited where a “steady flow” is desired .  Diaphragm pumps are very efficient in suction lift and, in some cases, could effectively be used to transfer water from a sump well below the the desired cistern location.

A more common use for a diaphragm pump in a rainwater collection system is a small air compressor used to keep large amounts of stored water from going anaerobic or with chemical treatment such as chlorine, if required.

Should You Use an External or Submersible Pump in Your Rainwater Collection System?

submersible-pumpAs mentioned in a previous post, centrifugal pumps are the most common type used in rainwater collection. Sizing of the pump is essential in finding the right pump to meet the needs for which the system was designed. A water cooled centrifugal pump is recommended for potable application. Friction, static head, lift,PSI, and GPM are factors that need to be considered in sizing your pump. Pumps are either submersible or external, and depending on the application, one could be better suited than the other.

Sump tanks are generally smaller than the cistern and their purpose is to convey water collected from the roof to a central collection tank, then pumped to storage. A submersible pump with a float switch is best suited for this application. As the sump tank becomes full of collected water from the down spouts, the float switch turns the pump on to transfer water to storage. When the water level in the sump drops the float switch to the down position, the pump turns off. Submersible pumps for this application “MUST” be water cooled. The use of an oil cooled submersible pump is not considered NSF for potable use. The water cooled, submersible centrifugal pump needs to lift to the top of the cistern, whether the plumbing is external or internal. A larger pump will be required if the pump is not able to meet the lift requirements. Unlike external centrifugal pumps, which need to be primed and maintain that prime during and after pump cycle, submersible pumps, if completely submerged, will maintain a constant prime for operation.

Submersible pumps can be 120 or 220 volt and can be AC or DC. Solar power with battery backup can be used for sump pumps allowing an “off grid” application. Care must be taken to insure that the pump’s electrical needs are met from the power supply in order to protect the pump from damage.

External centrifugal pumps are generally used to transfer collected water from storage (cisterns) to use. This can be a “on demand” booster pump or a dynamic pump with control of suction flow to a pressure tank. A booster pump needs to be primed before operation and able to maintain that prime after the pump shuts off. With an external centrifugal pump, suction lift is limited. This type of pump should not be higher than the stored water low level, allowing head pressure to feed the pump, rather than the pump pulling water up to its level. AC, DC, or solar can be used for pouring the pump. This style of pump is generally water, air cooled and should be protected from freezing.

Whether you are looking into a submersible or a external pump, centrifugal pumps offer a wide range of horse power, GPM and PSI. Sizing your pump will determine its efficiency and longevity.