RAINWATER CATCHMENT & FILTRATION

Rain water catchment is a sustainable way to use fresh water without depleting environmental water sources.  The following products are components of a Tiny Off-Grid House rain water catchment water treatment system.  The filtered rain water will be used for potable consumption, washing and micro-irrigation.  The products are listed and described in their respective order of plumbing from the inlet source water downstream to water storage.

The Tiny Off-Grid House water treatment system “filters” rain water; or if necessary, treated potable water. Since water is such an essential resource needed for life it is expected that potable water from alternate sources, other than rainwater, may have to be utilized.  However, the water treatment system is not intended to “purify” contaminated water or water from polluted rivers, streams, lakes or leaching lead distribution pipes . . .  No antimicrobial chemical agents, like impregnated silver ions, iodine, activated Aluminum Oxide are used to inhibit or reduce microorganisms or change the water chemistry.  The water treatment system should meet NSF/ANSI residential water treatment standards: 42 (aesthetics, taste and odor), 53 (health related concerns) for drinking water treatment units, 2018.

The water storage & distribution plumbing is situated in the stern, adjacent the bathroom, to shorten the distance the hot water has to travel from the water storage tank to the electrical on-demand tankless water heater located in the bathroom and to other water outlet appliances—water loads—and facilitate discharge of grey water through the shortest route on the port side using the worlds oldest & cheapest technology; gravity.  This is also strategic since most RV & campsite utilities are usually located on the port side.

A rain water catchment system is considered a safe renewable water source.  Although much cleaner than ground water, rain water still needs to go through some form of a water treatment system since rainwater can adsorb micro particles of dust and carbon dioxide —Produced by respiration and from the burning of carbon and organic compounds—the latter from the atmosphere as it falls down creating carbonic acid (CO2 + H2O = H2CO3); at @ 5.6 pH.  However, the absorption rate will vary by region.  Rainwater in urban or rural regions with coal powered plants will have a greater rate of carbon dioxide adsorption.  Other contaminants may come from the composition of the roof material, dissolved organic compounds (DOC), sealants, contamination from animal feces or pollen requiring water filtration and maybe even disinfection to meet the Environmental Protection Agency (EPA) clean safe drinking water standards.

Rain water harvesting should only be preformed on metal roofs that will not contaminate the water with debris, rust, paint, oils . . .  Unlike copper, an Aluminum metal roof, like the kind that will be installed on the Tiny Off-Grid House, should not leach metal in to the water through a process called osmosis.  Leached Zinc from galvanized roofs are harmful not only to humans but also to vegetation since it is a herbicide. 

Water catchment on a metal roof and solar panels are better than roofs made of other materials that may contaminate the rainwater.  Harvesting rainwater from roofing material made of wood, lead, copper tin, galvanized (Zinc) or wood (usually treated with fire retardants), antimicrobial paints (Zinc & Copper) to combat bacterial growth from fecal material or algae and moss growth should be avoided.  Also, debris are less prone to adhere to a metal roof. 

Water samples should be collected directly from the rainwater, free-fall catch, on the the metal roof and post filtration and disinfection for comparisons, then sent to a certified laboratory to test for bacteria (CFU’s), endotoxins (LAL’s) and for metals to confirm they meet Environmental Protection Agency (EPA) clean drinking water standards.  Even if all precautions are taken, it may still be wise to allow atleast one or two good rain falls to first flush a newly installed roof and rain water catchment system before collecting household water from it.

The rainwater catchment system will incorporate a detachable downspout with an inlet leaf & debris screen and water diverter running along the starboard side of the roof, down into a “food grade” container.

Calculating Your Water Catchment:

Roof catchment area (sq ft) x rainfall depth (inches) x 0.623 (conversion factor) = Harvested rainwater (Gallons). 

If water is supplemented from a pressurized water hose, the same level of water filtration, if not more, as with rainwater maybe needed. If so, the first line of defense in water purification is the use of the Camco Inline TastePURE KDF/Carbon Water Filter with Flexible Hose Protector (#40043)

The Inline Water Filter has a potential to clog easily reducing water inlet pressure downstream; so frequent replacement is necessary.  

The water hose should have a pressure regulator attached to reduce high pressured municipal or RV water systems to a consistent 40 - 50 PSI without fluctuations.  In freezing temperatures a heat wrap for the feed water hose maybe necessary. 

The Camco Inline filter is connected to a pressurized water hose that attaches to a city water inlet hatch with a secured door to protect the main port of entry for the feed water.

The spin-down sediment filter has a 50 micron stainless steel mesh filter to prevent large particles from entering the water treatment system downstream.   The mesh contains siliphos softener which is a natural milk thistle seed extract that helps prevent hard water damage and corrosion.  Also, a backwash line to drain facilitates easy maintenance and cleaning 

The 3-Stage 20” water filters are a series of point-of-entry whole Tiny Off-Grid House water cleaning system.  

The EPA has established National Primary Drinking Water Regulations (NPDWRs) that set mandatory water quality standards for drinking water contaminants.  These are enforceable standards called “maximum contaminant levels”  (MCLs) which are established to protect the public against consumption of drinking water contaminants that present a risk to human health.  An MCL is the maximum allowable amount of a contaminant in drinking water which is delivered to the consumer.” https://www.epa.gov/sites/production/files/2016-06/documents/npwdr_complete_table.pdf

Filter Housing Maintenance:

Maintenance of the filter housing includes, but not limited to, checking for leaks, reapplying a water based lubricant to the o-rings on the top of each filter housing during each filter replacements.  It is recommended that opaque filter housings be replaced after every 10 years of use.

Use the wrench only for removal of the filter housing—never to tighten—the filter housing should only be hand tightened. The subsequent water pressure and o-rings will do the rest to seal and prevent water leakage. When removing, it maybe necessary to first activate the pressure relief valve, on top of each filter housing, or open the outlet valve to facilitate removal of the filters.

Also cleaning any grime deposits from the inside of each filter housing using a damp disposable cloth and mild detergent. 

Each of the disposable 20” x 4.5” filters have a specific purpose, yet have a symbiotic relationship to the others as a force multiplier to clean the water. The pre-filtered water enters the filter housing from left to right.  

The biodegradeble organic materials or media composing the filters can be disposed as, non-hazardous, recycled waste.

Sediment Filter: 

The first of the three 4.5” W, 20” L filters is a 1 to 5 micron sediment filter, that is responsible for removing sediment and particulate matter from the feed water.  

Particulate matter, like insoluble Ferric Iron (Fe +++) rust are trapped as the water travels from the filter outer perimeter to the inner core; then up to the next series of filters downstream; subsequently, extending the life of the carbon filters downstream.

Sediment Filter Maintenance:

Replacement of the Sediment Filter, 1 micron, may be more frequently due to the small pore size becoming clogged with particulate matter.  Large particulates like insoluble Ferric Iron (Fe +++) rust can easily clog the sediment filter.

Carbon Block Filter: 

The second stage filter is a carbon filter 20” L x 4.5” W (508 mm x 114.3 mm), 1 µm (nominal) filtration , 6 pounds per square inch (PSI) @ 4 gallons per minute (GPM) (0.41 bar @ 15.2 Lum) at temperature ranges of 40 - 180 ºF (4.4 - 82.2  ºC) are made of compacted chemical free, acid washed, renewable coconut shells called Granulated Activated Carbon (GAC) block that trap: particulates, herbicides, pesticides, organics chemicals, volatile organic compounds (VOCs) that impact the taste, color and hydrogen sulfide odors in water; along with both free chlorine (Bleach) and chloramines (Bleach + Ammonia NH3) through a process of adsorption—not to be confused with absorption.  (Absorption is like a sponge soaking up water, while adsorption is like a metal paperclip adhering to a magnet).   The rate of adsorption depends on the water temperature, level of Total Dissolved Solids (TDS) and pH.  The chlorine disinfectants are added by the municipal water authority to prevent the proliferation of waterborne pathogens like guardia and cryptosporidium. Inorganics such as lead, mercury, microplastics are also known to be filtered by the GAC block filter.  Each GAC filter has a filtering capacity of 150,000 gallons of water before replacement is due.

The municipal water authority may add other chemicals to maintain the pH level of the water to prevent corrosion of the distribution pipes—especially lead pipes.  Also, flocculants, like Aluminum, maybe added to clear turbidity in the water for aesthetic appearances.

The series of carbon filters reduce up to 99% Free Chlorine to a minimum level of < 0.5 mg/L and chloramines to a minimum level of < 0.1 mg/L. Chlorine/chloramines are disinfectants added to water systems to protect against waterborne microorganisms such as guardia, cryptosporidium, cysts, along with odors and up to 3 ppm of dissolved soluble Ferrous Iron (Fe++) from the water.  This prevents the metallic taste Ferrous Iron causes in water.  (NSF/ANSI Standard 53 for turbidity & cyst reduction)

Activated carbon filters have been known to reduce lead levels to less than 1 ppb in water; depending on the number of total dissolved solids (TDS), water temperature, iodine number, particle size of carbon, water contact time with the carbon filter, water pH level. Exposure to lead, found in drinking water, can cause learning disabilities and behavioral disorders in children.  Animal companions and plants are not immune from the effects of water contaminated with lead.  Water can become contaminated by lead pipes, used for distribution, when the pipes leach lead due to the low pH of the water. GAC is also known to remove 99% of radon gas dissolved in water.

How It’s Made:

The acid washed coconut shells are treated with oxygen to open up millions of tiny adsorbent pores and crevices creating carbon particles with a large adsorbent surface area (H-carbon). The charcoal is carbonized at 1470 - 1830° F (800 - 1000° C) and cooled in an atmosphere absent of oxygen.  The pore size of the GAC range from 1 - 5 microns.  The smaller size pores size are effective at removing microorganisms from the water; but not viruses—since they are too small.  The filters usually range from 20 to 40 nanometers.

The iodine rating is the capacity of GAC to remove organics.  This is the amount of iodine, in milligrams, absorbed by one gram of GAC; at standard test conditions.  The higher the iodine number, the increased adsorptive capability of the GAC.  For our purposes, the iodine number must be > 900.

Unlike a loose filled “granular” carbon filter, a carbon “solid” block" made from compressed carbon powder, is more denser, forcing the water to have an increased contact time—which is the time it takes the water to flow through the carbon filter.  The pretreatment water should have contact with the carbon surface area of a carbon filter for a “minimum of 5 minutes each. (ANSI/AAMI RD52:2004 Requirements as adopted by Reference 42 CFR 494.40 (a) 5.2.5 Carbon adsorption: banks of tanks V193).  The pretreatment water should be filtered “at the slowest possible rate tolerable to increase contact time.  Two 20” long carbon block filters in series provide a total contact time (Empty Bed Contact Time) of 10 minutes through the series of carbon tanks.  Another benefit of a carbon “block” is that it eliminates the formation of channels or bypass that can occur in loose filled granular carbon filters which causes water streams to avoid contact with the GAC.

The microscopic crevices found in the activated carbon creates a huge surface area that greatly increases the effectiveness of the GAC Total Chlorine reduction and some large microorganisms.  The total surface area of a single gram of activated carbon can be more than 1,000 sq. ft. if spread out or one teaspoon is equivalent to the area of a football field.

The carbon block filter can be removed easily from inside the filter housing and disposed as recycled waste; unlike a loose filled carbon tank which requires a mechanical back-washing system to clean and reshuffle the GAC granules to prevent the formation of channels among the loose packed GAC.

If two carbon filters are installed in series, the first filter is known as The Worker or Primary Filter.  The Primary Filter performs most of the work of removing Total Chlorine from the municipal water while the second GAC filter is called the Polisher or Secondary Filter.  The Secondary filter serves as a backup to the Primary filter.

The water treatment system sediment and carbon solid block filters have the ability to handle a variety of inorganic heavy metals (Lead Pb, Mercury Hg, Copper Cu, Cadmium Cd) if they remain in a particulate size large enough to be trapped by the filter media or if dissolved in the water they can be adsorbed in GAC pores. Ofcourse mitigating falters include water pH, total dissolved solids, temperature and hardness.  

Most heavy metals are not naturally endemic to water.  They are introduced through municipal water chemical treatment, distribution pipes, household copper pipes and lead soldering.  The majority of the problems associated with heavy metals can be avoided if the water plumbing avoids the use of Copper piping, Lead solder and chemical water treatment.

According to the E.P.A. atleast 20% of human lead exposure originates from municipal drinking water. In July of 2021, the New Jersey State Senate passed Bill A5343/S3398 that requires the water authorities to inspect their service lines (From the main water pipes to where it enters a house) within 6 months for signs of lead pipes; then replace them within 10 years.

Carbon Filter Maintenance:

An elevated PSI reading on the inlet side of the Primary Filter pressure gauge indicates a clogged Filter(s).  When replacing two consecutive carbon filters of the same type , dispose of the Primary Filter, then transfer the Secondary Filter from the right to left —middle position— now making it the Primary Filter.  Install a new Secondary Filter. 

After every filter replacement, a flush to drain “must” be completed to evacuate excess air and loose activated carbon debris. This is accomplished by closing the main valve after the water treatment filters system and opening the flush valve.  Flushed water is diverted from contaminating the clean water holding tank and out to the drain. 

Cons Of Carbon Filters:

Carbon filters can not efficiently remove dissolved inorganic contaminants and heavy metals such as calcium, magnesium, cadmium, copper, fluoride, mercury, nitrates and salts . . . Nor can the GAC, 0.3 microns, filter out viruses because the virus particle can be as small as 0.01 microns.

Pretreatment water in the GAC filter is susceptible to heterotrophic plate count (HPC) non-pathogenic bacteria since the chlorine disinfectant is removed from the treated water.  The health effects, if any, on healthy individuals are unknown but there maybe unknown potential health risk for vulnerable individuals like the very young, elderly, or immune compromised . . .  The potential development of HPC can be mitigated by scheduling frequent disposal of the “primary” GAC block filter and disinfection of the inner filter housing; following manufacturers recommendations.

Kinetic Degradation Fluxion (KDF) filters do not reduce total dissolved solids (TDS) like a RO system; instead TDS are exchanged for harmless compounds through an ionic exchange.

Lead/Iron Filter: 

The last of the trio of water filters is a Kinetic Degradation Fluxion (KDF) lead, iron & manganese filter which reduces lead to below 15 ppb, iron in excess of 5000 ppm gallons. A KDF filter is made of catalytic carbon and high purity ionically charged Copper and Zinc granules.

Other metals that this filter can reduce includes, but not limited to: calcium, nickel copper, zinc, mercury tin, mercury . . . 

Lead/Iron Filter Maintenance:

The maintenance of the lead/iron filter is the same as for the previous two filters.  Depending on the water quality, replacement can depend on operator preference or ultimately the delta pressure between the in/outlet PSI pressure gauges.  The delta pressure is the difference in PSI between the two gauges.  A clogged filter will be exhibited by an elevated PSI reading on the inlet gauge compared to a lower PSI reading on the outlet gauge.  (Inlet gauge 40 PSI - outlet gauge 34 PSI = a delta pressure of 6 PSI)  If the filter normal delta pressure is from > 1 to 5 PSI then this filter will require replacement.

Water Softener:

A water softener removes Calcium (Ca) and Magnesium (Mg) from hard water using Sodium (Na) pellets in brine water through a process called ionic exchange.   The Ca & Mg cause scaling to filters and clogs shower heads.  The Ca & Mg has an affinity for the resin beads which displaces the resident Na as it flows down stream.  The water softener can clean an regenerate itself when high concentrations of Na overwhelms the Ca & Mg evicting them off residency from the resin bead. The water softener can also absorb dissolved iron from the water.  However, a byproduct of the ionic exchange is elevated levels of sodium in the outlet water which can impact health and plant irrigation. 

Subsequently, a water softener system will not be utilized in the Tiny Off-Grid House.

Reverse Osmosis:

The ultimate choice of a water treatment system will depend on local water conditions and may need to include more than one of the components described above. Water that is microbiologically unsafe, or of unknown quality should be disinfected before use. For water purification, not to be confused with water filtration, a “Reverse Osmosis (RO)” system (NSF/ANSI Standard 58 For Reverse Osmosis) is one of the best known methods that uses mechanical pressure to reverse the flow of water in the natural process of osmosis so that water passes from a more concentrated dirtier solution to a more cleaner dilute solution through a semi-permeable membrane; that has a pore size of approximately 0.0001 micron” as per The CDC.  The average R.O. membrane is a thin film composite (TFC) made of polyamide.  A R.O. system can reject 95-99% of charged ionic particles (e.g. aluminum) salts, bacteria, endotoxins and viruses . .

The R.O. membrane has to be disinfected regularly to prevent bacteria from growing on it and remove scaling from calcium buildup.  However, chlorine (Bleach) and chloramines (Bleach + Ammonia) cannot be used as a disinfectant on a R.O. membrane because they can permanently damage the fabric of the RO membrane.  If “chlorinated” water is used carbon tanks must precede the R.O. system to remove the chlorine/chloramines from the upstream water.  A R.O. system discharges, or rejects, a portion of the water it consumes to flush out the contaminants from the water.  Reverse osmosis is not sustainable for an off-grid rain water treatment system in which water conservation is a priority.  Also, a considerable amount of electrcity will be needed to power the R.O. system.

Ultraviolet Irradiation:

Another option is Ultraviolet irradiation at 185 nm to attack the DNA of bacteria impacting their ability to multiply.

The stainless steel chamber holds a 11watt, UV lamp.   Although the UV system uses a 110 volt, 0.41 amp transformer, energy usage is mitigated by an automatic built in flow sensor that turns on/off when water is detected.  Still the energy consumption may burden an off-grid electrical system compared to its benefits; if necessary.

Point Of Use Filtration:

A Brita® water pitcher or dispenser with longlast filter is a welcome accessary to a water treatment system. Brita® * filters are not intended to be used “with water that is microbiologically unsafe or of unknown quality without adequate disinfection”  According to Brita® their Longest filters—without the aide of a water treatment system—can remove particulates (Class 1), chlorine, 99.6% of lead (pH 8.5) mercury . . . at water temperatures 0 ºC/32 ºF Min, 29 ºC/85 ºF  2º F  Max. Note, hot water should not be used with Brita® Long last filters.  

The Brita® 25 cup capacity “slim" dispenser with Long Last filter can conveniently fit inside a refrigerator keeping water cold, without taking up a lot of shelf space.  According to Brita® a household using this water system can prevent up to 1,800 standard 16.9 oz plastic water bottles each year from entering landfills or the ocean.  It is estimated a plastic bottle discarded in the ocean takes 450 years to decompose; all the while breaking down in to smaller and smaller micro plastics that get ingested by marine life whom eventually end up ingested by humans higher up the food chain.

Another environmental benefit is Brita® dispensers, filters, faucet systems are all recyclable through their partnership with TerraCycle.

Clean Water Storage:

Once the water is filtered it is stored ready for use in a clean water holding tank located in the stern of the Tiny Off-Grid House. The clean water holding tank will be a Food and Drug Administration approved (U.S. FDA Regulation 21 CFR 177.1520) food grade, polyethylene resin tank constructed in one seamless piece that holds 55 gallons of filtered (post treatment) water for domestic use weighing 458.7 pounds at 62 F (17 C) when full (Note 1 Gal = 8.34 Lbs). The walls of the water tank must be thick enough to avoid bulging at the sides when full; along with baffles to prevent sloshing of the water.

* Trade names and images are used for informational & comparison purposes only. No endorsement is intended, nor is criticism implied of similar products not named.

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