1. What kind of water filter did the TAP study provide?
The brand of filter that the study provided is a DUPONT FM 350 Deluxe Faucet Mount Filter System. The filter itself contains granular activated carbon (GAC). Many common home filters, including countertop pitchers (such as Brita or PUR) and faucet or sink attachments, use a GAC filter. These filters are good for improving the taste of the water, removing microbial contaminants and removing or reducing some chemicals.
2. How often should I replace my water filter cartridge?
It is important to change the filter cartridge every 3 months. If you leave the old cartridge in for too long without replacing it, the filter can become too full of contaminants and can dump them back into the water, making the water quality worse. Also, bacteria can eventually grow on the filter. If you are using the filter provided by the TAP study, replacement cartridges can be purchased through Walmart or Amazon for about $20.
3. What should I use to remove other contaminants?
If you decide to purchase a water filter, it is important to choose one that is independently certified to remove the contaminants you are concerned about. All water filters sold in California must be registered under the California Residential Water Treatment Devices Registration program. This program ensures that filters have been tested and certified by an independent, accredited organization to validate that the filter in fact removes what the manufacturer says it does.Effective water filters also have a certification called the National Sanitation Foundation (NSF)/American National Standards Institute (ANSI) certification. There are two main certifications, one for water aesthetics, such as taste (NSF/ANSI Standard 42) and the other for water safety (NSF/ANSI Standard 53). There are also other certifications for specific types of filters or specific contaminants. You can look up filters in the NSF database (https://info.nsf.org/certified/dwtu/) to see which ones are effective for specific contaminants in your water. Below is information about the main types of filters.
Granular Activated Carbon (GAC) Filter
How it works
- As water passes through, most contaminants are absorbed onto the carbon and remain in the filter.
Effective against
- Taste, odor, volatile organic compounds (VOCs), disinfection byproducts, many pesticides and industrial chemicals, and some per-and polyfluoroalkyl substances (PFAS).
Not effective against
- Generally does not remove minerals, salts, and dissolved inorganic substances like nitrate. Some PFAS compounds are reduced but not fully removed.
Other considerations
- If not replaced regularly, filters can saturate and can dump contaminants into water.
- GAC filter pitcher or faucet system costs less than $40. Replacement filters cost about $5 each.
- Under-sink GAC systems cost $100-$200 and are relatively easy to install. Replacement filters cost
Ion Exchange Filter
How it works
- Ions are minerals and salts such as sodium, chloride, sulfate, and arsenic. This filter users a chemical process to replace unwanted ions in water (such as nitrate, fluoride, sulfate, arsenic) for other less harmful ions (such as sodium, potassium or chloride).
Effective against
- Nitrate, metals, arsenic, perchlorate, other minerals, some PFAS
Not effective against
- Bacteria, most industrial chemicals
Other considerations
- Countertop water filter with ceramic filter and ion exchange media costs about $100.
- Whole building systems are expensive (normally $1000+).
- Can waste water and be costly to operate. They require multiple bags of salt and need regular maintenance.
Distillation Filter
How it works
- The water is boiled to kill any microbes. Boiling produces steam which rises and is cooled and converted back into a liquid.
Effective against
- Heavy metals such as lead, bacteria and viruses, minerals such as nitrate fluoride, and sulfate, some toxic organic chemicals.
Not effective against
- Many industrial chemicals and pesticides
Other considerations
- Household/countertop water distillers usually cost $100 - $500.
- Plumbing distillers can be installed into existing home plumbing. They distill water as you need it.
- It is important to maintain these filters regularly by draining the sediments that accumulate in the boiling chamber.
- These cost between $300 to $1000 and will produce water for about $0.25 a gallon.
Reverse Osmosis (RO) Filter
How it works
- Water pressure pushes tap water through a membrane that stops most contaminants from passing through. Fresh water is produced and waste water (brine) is left over. Look for a filter that is certified under NSF/ANSI Standard 58. The filter may clog if there is no additional filter, so these systems typically also include a GAC filter.
Effective against
- Dissolved solids (minerals, arsenic, etc.), nitrate, fluoride, many PFAS, pesticides and industrial chemicals.
Not effective against
- Viruses. Bacteria can sometimes penetrate these filters if they are not well-maintained.
Other considerations
- RO filters waste a lot of water. About 3 gallons of water is wasted for every 1 gallon filtered.
- Under-the-counter RO systems can cost between $200-$500 and replacement filters are expensive.
- Whole house RO systems are typically used for treating a large volume of water (150-50,000 gallons). These cost between $1000-$5000.
4. What about other treatment options?
Other water treatment options include water softeners and UV light. These systems do not remove chemical contaminants.
Water softeners
- This treatment is used to remove minerals to make the water softer. They do not remove bacteria or chemicals. Some softeners put salt into the water and should not be used by people on salt restricted diets or as drinking water for pets. Some municipalities have outlawed some water softeners.
Ultraviolet (UV) disinfection
- UV disinfection is used to kill microorganisms like bacteria and viruses. This does not remove other contaminants.
5. Will boiling my water make it safe?
Boiling your water will kill most bacteria and remove some contaminants such as disinfection byproducts, and volatile organic compounds. But boiling water can increase other contaminants such as lead, arsenic, and nitrate by concentrating them in the water.
6. Should I buy bottled water or water from a vending machine from a supermarket?
Bottled or vended water is generally not as well-tested or well-regulated as tap water. It is expensive and usually unnecessary to buy water in California.
Some bottled water and most vended water is produced by treating tap water, including water from local sources.
Store-bought water can collect toxic chemicals from the plastic in which it is bottled or stored , especially if the water is left in the heat at a store before purchase, or later in a car, or at home.
We recommend only buying water if your water contains contaminants at unhealthy levels and if an affordable filter will not work. In general, public water systems are reliable and ensure that your water meets all legal standards and provide you with information about your water quality. The alternative of bottled water can be useful for incidental or temporary purposes.