Pure Water Occasional, February 25, 2018
In this late February Occasional you'll hear about TDS creep, nickel in water, weight gain from PFAS, a grievous water billing mistake, and people who are giving up plastics for Lent. Hear about Cape Town's water dilemma, earthquakes in Oklahoma, radium in Texas water, and water rationing in a refugee camp. Learn the basics of rainwater treatment, find out how RO booster pumps and spindown filters work, and as always, there is much, much more.
The "Spin Down" filter pictured above can handle high flow rates and very dirty water. Its function is to remove larger sediment (such as sand) from the water stream.
The unit is installed into a horizontal water line with the black-handled ball valve pointed down. A hose can be easily attached to the bottom of the valve to facilitate drainage.
As sediment-filled water enters the filter it is swirled rapidly in the clear chamber around the center core, which is a filter screen. Heavier particles are spun to the outside wall and drop out of the water stream. Water flows through the filter screen and exits the out port of the filter.
When sediment has collected in the filter, it can be easily blown out by opening the ball valve. Full line pressure will purge the filter of collected sediment and rinse the screen.
The replaceable screens have a very long life span, as water filters go. Screens are measured by mesh size (the number of holes per square inch in the screen material). The larger the mesh number, the tighter the screen and the smaller the particles it will catch. For example, a 250 mesh screen catches smaller particles but is easier to clog as compared with a 100 mesh screen.
Filter screens are replaceable in most units of this type. Measurement can be expressed in microns, but are more usually referred to by mesh.
Common mesh sizes for spin down filters with micron equivalents are as follows:
100 mesh equals about 149 microns
400 mesh equals 37 microns
Should You Worry About Nickel in Your Water?
Nickel is a silvery white metal. It is found in most water, usually at the level of about one part per billion. Although it is a suspected carcinogen when inhaled, there is no evidence that it poses a threat when ingested orally. In some it produces allergic reactions.
The EPA has no proposed maximum contaminant level (MCL) for nickel.
Removel from water can be done by a strong acid cation exchanger, or water softener. Activated carbon reduces nickel and reverse osmosis removes 97 to 98 percent.
The nonprofit Environmental Working Group (EWG) evaluated data from a five-year study that ended in 2015 and found radium in water in all 50 U.S.states.
The state with the most widespread contamination, according to EWG, is Texas; where more than 3,500 utilities serving more than 22 million people — about 80 percent of the state’s population– reported finding radium.
“Radium and radon are potent human carcinogens. Radium, via oral exposure, is known to cause lung, bone, head (mastoid air cells), and nasal passage tumors. Radon, via inhalation exposure, causes lung cancer,” according to an Environmental Protection Agency (EPA) fact sheet.
Radium is a contaminant with a relatively high EPA limit. California’s limit is much lower. A large number of U.S. water systems which pass the federal standards exceed those set by California. According to the EWG, “Almost all [states] exceeded California state scientists’ public health goals for two separate radium isotopes, set in 2006, which are hundreds of times more stringent than the EPA’s standard for the two isotopes combined. The elevated risk of cancer, as well as potential harm to fetal growth and brain development, decreases with lower doses of radiation but does not go away.”
Water Treatment for Rainwater
As water becomes scarce, rainwater collection systems are becoming increasingly popular.
After water is collected and stored for later use, water treatment is essential. This usually takes the form of filtering out large particles, then treating for microbiological safety. If the water is contaminated with chemicals from its collection process (for example, roofing materials if the water is collected from a roof), then a good carbon filter should be added to the treatment.
Filtering for sediment can be either with cartridge filters or, if there is a lot to be filtered out, a backwashing filter that filters down to 10 microns or so.
After elementary filtration to remove particulate, it is critical that some form of disinfection be used. This can be:
Chlorination, the old standby, followed by carbon filtration to remove the chlorine.
Ultraviolet (UV), which is probably the most popular single rainwater treatment. The water must be very clean when it passes the UV lamp to assure complete disinfection. UV has the advantage of adding no chemicals to the water. It should be the last stage in the treatment process.
Ozonation is an excellent disinfectant, but is a bit more challenging for the homeowner from the technical viewpoint.
Ultrafiltration (UF) is gaining popularity in rainwater treatment. UF filters down to about 0.02 microns—enough to remove cysts, bacteria and viruses. Again, water must be pre-filtered before the UF membrane to protect it from premature clogging of the ultrafiltration equipment.
Rainwater, with only the minimal treatment described above, can provide extremely good water. Its mineral content (TDS: Total Dissolved Solids) is very similar to that of reverse osmosis water.
The purpose of the reverse osmosis (RO) booster pump is to increase water pressure going into the RO unit.
Reverse osmosis is a pressure-driven process. Small residential RO units will theoretically operate on very low pressure - down to 35 psi, according to some membrane makers - but the reality is, you won't get a lot of water and the product water quality will be compromised if the unit runs below 45 psi. Low inlet pressure makes the unit produce more reject water, produce less drinking water, fill the storage tank more slowly, and produce lower quality water.
RO units run well on typical city water pressure of 60 psi, but they run even better with a small pump to boost the pressure to 80 psi or higher.
The picture above shows the three essential elements of the RO booster pump. The white object at left is the transformer. It plugs into a standard wall outlet and converts to the voltage (most commonly 24 volts) required by the pump. The large object is the pump itself. The third device is the pressure switch. It monitors the water pressure in the RO unit's storage tank and turns the pump off and on in response to storage tank pressure. The most common shutoff pressure for undersink home RO units is 40 psi.
The standard pump setup is shown above. The function of the pressure switch in the tank line is to shut off current to the pump when the tank pressure reaches a preset level. Default pressure settings usually provide around 80 psi pressure going into the RO unit and shut off production when tank pressure reaches 40 psi.
Do You Need a Booster Pump?
Most city water reverse osmosis users have enough city water pressure to run their RO unit nicely and they do not need a booster pump. For example, if your city water pressure is 60 psi or more, there is little to be gained by adding a booster pump. If your pressure is 50 psi or less, however, a pressure boost pump will give your RO unit more zip. You'll have more water at a higher pressure in the storage tank, and the tank will fill faster. The increased pressure will also improve the economy of the unit (it will run less reject water to drain) as well as the quality of the water. RO units thrive on pressure.
Are All Pumps the Same?
Manufacturers often designate pumps by the gallon-per-day output of the RO unit. With the Aquatec 6800 pump pictured above, the recommendation is for use with units with membranes that put out up to 50 gallons per day. For larger membranes, another model, the Aquatec 8800, is recommended.
TDS Creep with Aquatec Permeate Pump
by Gene Franks
The permeate pump has become a popular option for undersink reverse osmosis (RO) units. The “pump” doesn’t increase inlet pressure, as an electric booster pump does, but enhances RO performance by isolating the RO membrane from back pressure from the storage tank. It uses energy taken from the brine (drain) flow to power the product water (permeate) into the pressurized storage tank. The permeate pump saves water, no doubt about it, and is assumed to improve water quality, as measured by TDS performance, as well.
One of the controversial issues with the permeate pump is whether it should be installed with or without a standard auto shutoff valve (ASO), the device that turns standard RO production off when the unit’s storage tank is full.
Non-electric permeate pump
If installed without a shutoff valve, the pump itself shuts down production when the tank is full. With this arrangement, the tank is filled to almost 100% of the pressure of the tap water. The high tank pressure is especially advantageous in low pressure situations, such as wells set up to send pressures as low as 30 or 40 psi to the home.
If the permeate pump is installed with the regular shutoff valve, the valve shuts down production when the storage tank pressure reaches about 2/3 of the tap water pressure.
The reason most permeate pumps are now installed with the ASO in place, in spite of giving up a little pressure at the faucet, is to combat a phenomenon called “TDS creep” that occurs when the RO unit sits unused. Without the ASO to form a physical wall between incoming tap water and the RO membrane, the dissolved solids count “creeps” upward because the natural forces of osmosis are still at work.
TDS stands for “total dissolved solids” and the TDS count is a theoretical sum of all the minerals dissolved in the water. Testing TDS is a standard way to evaluate reverse osmosis performance. The lower the TDS reading, the better the unit is working.
I decided to give the TDS creep problem a real world test with my home RO unit running with three different configurations to see if much dreaded TDS creep really matters significantly in home units. The chart below shows the three formats and the results.
I took 16 tests in each of three categories, all in the morning, testing the first water out of the unit after a night of inactivity. TDS creep occurs when the unit is not producing water. In all, the testing spread over 12 consecutive days. I tested the first glass, the second glass, the third glass, and then emptied the tank half way and took a test there. As expected, the first and second glasses usually but not always had the highest TDS readings no matter what format the RO unit was arranged in.
Testing wasn’t done with high dollar lab equipment but with my trusty HM TDS-3 handheld tester, the same tester we send out with our Black and White RO units.
A tap water TDS reading was taken before each group to provide a “base line” and results below are expressed as “% rejection” rather than actual TDS numbers.
“Percent rejection” means tap water TDS minus RO TDS divided by tap water TDS. It expresses the percentage of the total dissolved solids (minerals) in the water that are being rejected by the membrane. The higher the percentage, the better the membrane is working.
The column on the right is the significant figure. It shows the average of all 16 tests taken in the category.
|Lowest Reading (% rejection)
|Highest reading (% rejection)
Average reading (% rejection)
|Permeate pump with auto shutoff installed
|Permeate pump with auto shutoff absent
|Standard setup: auto shutoff, no permeate pump
As expected, the “first water out in the morning” TDS performance of the unit with permeate pump was better with the shutoff valve than without. It was totally unexpected, however, that the best performance of all was the standard setup unit with the conventional shutoff system and no permeate pump. I have no explanation for this, but I should mention a couple of variables. One is that the membrane used is the GRO 50/50, a stingy water-saver that puts out a much reduced brine flow to drive the pump. The pump seems to run fine with the GRO, but starvation of brine water to power the pump might matter. Also, the pump itself is an older version ERP 1000, and the newer, quieter ERP 500 might be a better match for the membrane.
The final word, though, is that although the TDS performance of the permeate pump unit with the shutoff valve seems a bit better, for residential units with lots of stop and go use, I doubt that the difference is worth worrying about. This tiny trial certainly doesn’t give a definitive answer, but I suspect the result from my home unit is typical of what happens in most home installations.
Fluorinated chemicals slow down metabolism.
A new study has linked PFAS in water to weight gain and the inability to lose weight.
Series of earthquakes seem to be result of human activity.
Because of hydraulic fracking, parts of Oklahoma are considered to have the same earthquake risk as California.
Water utility switches meters and bills wrong customer for years
Tim McMillan bought a home for his small family in San Diego in 2002 and always felt that his water bills were way too high. He complained without success. It was recently discovered that the city's billing system had switched his meter readings with that of his neighbor, Joe Zumbo. The switched meter error had been going on since at least 1994 and occupants of the two properties had been paying each other's water bills for well over 20 years.
Joe Zumbo's water hookup furnishes Joe's home as well as three one-bedroom apartments.
The city has offered Tim $2,600 in restitution, but Tim contends they owe him at least $9,000.
Source: Water Online
Giving up plastics for Lent
A large part of the world's plastic waste (estimates range from five million to 13 million tons per year) ends up in the oceans. Circulating currents have created immense rotating patches of waste, mostly plastic, in subtropical regions. Seeing plastics as a threat to mankind, the Church of England has added plastics to the list of indulgences that Christians might like to give up during Lent.
Source: The New York Times
Refugees allotted five gallons of water a day
Zaatari is the biggest refugee camp in Jordan. It houses 79,000 Syrian refugees. Each is allotted about five gallons of water per day for bathing, cooking, cleaning, and drinking.
Insecticides found in tributaries of Great Lakes
Neonicotinoids are the most heavily used insecticides on the planet - designed to attack the nervous systems of insects and protect crops from damage. Once thought to be relatively innocuous to wildlife higher up the food chain, scientists are increasingly reporting toxic effects. U.S. scientists found neonicotinoid insecticides in about three-quarters of samples from ten major Great Lakes tributaries.
Cape Town is Set to Become the First Major City to Run Out of Water
The city predicts that, based on current supplies and water use, Cape Town will run out of water on April 22 of this year. This upcoming “day zero,” as officials are calling it, is forthcoming despite already tight restrictions on water use for residents.
Cape Town’s four million residents are now only allowed 23 gallons of water per day. Next month that goes down to 13 gallons. Compare that to the average American who uses around 100 gallons daily. Thirteen gallons doesn’t allow for much — a 90-second shower, a quick toilet flush, basic dishwashing, weekly laundry, and a large bottle of drinking water.
Meanwhile, local farmers have only been able to plant a fraction of what they normally would. And this would decrease even more, potentially down to nothing, if taps are turned off entirely.
Beyond restricting water use, there seem to be few solutions in sight. Adjacent to the ocean as it is, Cape Town has explored desalination options. But it’s doubtful that this will solve the problem in time.
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Thanks for reading and be sure to check out the next Occasional!