DEAR DR. BLONZ: With all the attention being given to safe water and the events in Flint, Michigan, I wanted to know the differences between the types of filtration and disinfection performed by cities and personal water systems that hook on the water tap, or those that go into pitchers that stay in the refrigerator. Is chlorine safe for city systems? Can we rely on those home systems to filter out all the unwanted substances that make it to the tap? -- T.S., via email

DEAR T.S., Many factors can affect the safety of one's home water supply. For those living in industrial or agricultural areas, there can be risks of unwanted contaminants working their way into the groundwater. But even if the water meets all safety standards, as we have learned from the Flint experience, lead in pipes or faucets could be releasing that dangerous heavy metal into the water you use.

Chlorine is a very effective disinfectant, and it has been used for almost 100 years to help destroy micro-organisms that can infect public water. Guidelines must be carefully followed, as chlorine can react with natural materials or man-made pollutants to form mutagenic and carcinogenic compounds. These byproducts of chlorination have the potential to increase the risk of certain cancers, but it is doubtful that we will be seeing a cessation of chlorination anytime soon, as it represents the most economical and effective method of control at the present time.

There are plenty of home water treatment devices on the market, ranging in price from the tens to the thousands of dollars. It is only after you know more about the quality of your water supply that you can make a decision whether and what additional purification might be needed, and which system would be best suited to your needs. Inexpensive tap or cartridge filters, for example, can grab most of the chlorine and some heavy metals and improve the taste, but check carefully, as devices vary in their ability to handle lead.

The prudent first step is to request the annual report of water quality from the department that supplies the water to your house. The report should let you know where the water comes from, and there should be a complete list of potential contaminants, such as pesticides, herbicides, bacteria, metals, industrial chemicals and radioactive substances. These reports should be sent to the person paying the water bill, so if that is not you, you should seek out the appropriate individual and make sure that you are in the loop when the report is received.

There is always an option to have your water tested; this option might be of particular relevance to those using well water, or if your location is one subject to atypical factors, such as being close to a source of pollution that does not affect the entire water supply. If you decide to go this route, seek out an independent testing laboratory.

Whatever you are considering, I suggest you get up to speed on the issues by consulting the Environmental Protection Agency's page devoted to drinking water (www.epa.gov/your-drinking-water).

Send questions to: "On Nutrition," Ed Blonz, c/o Universal Uclick, 1130 Walnut St., Kansas City, MO, 64106. Send email inquiries to questions@blonz.com. Due to the volume of mail, personal replies cannot be provided.

DEAR DR. BLONZ: There are many companies offering vitamin and mineral deficiency tests, claiming to let you know which supplements you need. They test blood, saliva, urine and hair samples, in addition to asking questions about lifestyle and symptoms. In theory, these tests might take the guesswork out of finding the supplements one needs. But do these services work? -- W.S., Phoenix

DEAR W.S.: I remain skeptical of the deficiency tests you describe. Granted, vitamins and minerals play an integral role in bodily systems. Laboratories can determine if there is enough of a nutrient by observing or measuring specific tissues or chemical reactions. Such tests, however, are only useful in helping to determine if there is a stark deficiency.

A blood test, for example, might measure the activity of a particular enzyme that depended on the presence of a particular nutrient. Another approach might be to check for the occurrence of a particular symptom or abnormal metabolic byproduct that only appears when a particular nutrient is in short supply. In both these cases, you would detect a deficiency, but nutrient deficiencies of this type are uncommon. (Check tinyurl.com/jlz7unv for a report on the prevalence of nutrient deficiencies.) This is not the same as a test that can give you advice on the best vitamin and mineral regimen.

What about hair tests? In this approach, hair clippings are sent to a laboratory for analysis. The idea is that hair provides a running diary of our nutritional status at the time it was created inside the hair follicle. On the surface, this might seem to be a convenient procedure to provide useful clues to our inner workings. Hair analysis has been shown to be of value in uncovering certain toxicities, but it has never proven itself as a useful measure for determining an individual's unique dietary requirements. The same, unfortunately, can be said for saliva and urine tests.

The bottom line is that there isn't a precise way of determining an optimum intake level of any given nutrient for any given person. If anyone tells you otherwise, ask for evidence of their assertions.

DEAR DR. BLONZ: Are there certain B vitamins that stimulate the growth of fat cells? If so, which ones? -- N.K., Newark, New Jersey

DEAR N.K.: Fat cells, also called adipocytes, are distributed throughout the body, and they represent our energy reservoir. They grow in size as more fat, in the form of triglycerides, is dropped off for storage. Once they reach capacity, the body can make more fat cells. Once formed, fat cells are difficult to get rid of, remaining throughout our lives and changing only in the amount of fat they contain.

Fat cells, like all cells, depend on essential nutrients, but there is no evidence that B vitamins will stimulate fat cell growth, unless excess dietary energy continues to fill the existing fat cells. In that case, the issue is the intake of excess calories -- not vitamins.

Send questions to: "On Nutrition," Ed Blonz, c/o Universal Uclick, 1130 Walnut St., Kansas City, MO, 64106. Send email inquiries to questions@blonz.com. Due to the volume of mail, personal replies cannot be provided.

DEAR DR. BLONZ: Does putting milk in my tea (green, black or oolong) affect its antioxidant properties? I have seen and heard mixed answers on this topic. Please clarify it for me, as I do love milk in my tea. It would be very hard for me to stop this habit after so many years! -- T.L., Seattle

DEAR T.L.: First things first: Tea is a very healthy beverage choice. Population studies have suggested that compounds in tea can help reduce the risk of heart disease and other chronic ailments. Having at least one cup of tea per day, for example, has been associated with half the risk of developing a heart attack. This is thought to be due to the ability of certain compounds in tea to protect the fats in the blood (lipoproteins) from oxidation -- hence the term "antioxidants."

In relation to your question, the news is not all good, because a few studies have noted that the addition of milk seems to blunt the tea's antioxidant prowess. The final answers aren't all in, but the "milk effect" theory does seem to have some merit.

Take heart, and understand that tea is not the only antioxidant-rich substance available in our diets. As long as you have a healthful, plant-based diet overall, I encourage you to continue to enjoy your tea the way you like it. After all, eating and drinking should not always be viewed as a clinical prescription; enjoyment must have its place on the plate.

DEAR DR. BLONZ: Can soy products, such as soy milk, interfere with thyroid medication? -- R.S., Portland, Maine

DEAR R.S.: Yes, there is a valid concern here. The hormones produced by the thyroid gland regulate the metabolism in most cells of the body. Those who produce insufficient thyroid hormone are given medications that either stimulate greater production by the thyroid gland, or serve as a replacement for the hormone itself.

There is evidence that soy products can interact with the thyroid gland or its hormones, but not all soy products have the same effect. It doesn't appear that this would be a significant factor in adults eating soy as a part of a mixed diet. With thyroid medication, however, the story has an added level of complexity, because there can be a physical interaction that affects the absorption of the medication when soy is present at the same time.

It is always important to read the instructions and warnings for any medication you take. I say this because soy is not the only food with a potential interaction with thyroid medications. Many thyroid medications have specific instructions to be taken on an empty stomach to avoid potential interactions with foods. Be sure to consult your family physician, or a pharmacist, if you have any further questions.

Send questions to: "On Nutrition," Ed Blonz, c/o Universal Uclick, 1130 Walnut St., Kansas City, MO, 64106. Send email inquiries to questions@blonz.com. Due to the volume of mail, personal replies cannot be provided.