As University of Hawaii civil engineering professor Amarajit Singh detailed in an Island Voices op-ed, after a major storm it’s inevitable that raw sewage, storm runoff and other contaminants will leach into our municipal water supplies. Once the system has been compromised, it may be weeks until our water is potable again.

In short, if the city’s water system is out of commission, you’re going to be responsible for your own drinking water. In an emergency don’t count on Safeway or Costco. You could dip a cup in Manoa Stream, but it’s not a good idea. According to the state Department of Health, waterborne diseases such as giardiasis and leptospirosis are ubiquitous.

Fortunately, there are excellent filtration systems on the market.

As part of our research, my co-writer, Rob Kay, and I consulted with Samantha Biggers, a writer for Backdoor Survival, a respected blog that reviews emergency gear of every description. Biggers had product recommendations, some of which we tested.

The HydroBlu Go Flo Bag with Versa Filter ($40) is perfect for families or even if you’re solo. The whole package weighs 8 ounces and will fit in a coat pocket. It comes with a 10-liter bag with a spout that connects to a hose that feeds into the Hydro Blu Versa filter. To use it, hang up the 10-liter bag and create a gravity feed which will funnel water through the filter into a collapsible canteen (a 64-ounce bag) that is provided in the kit. Both ends of the filter are threaded so you can attach them to a standard disposable water bottle.

The kit also comes with a “bucket adapter,” a little spout that easily can be fitted on the bottom of a 5-gallon bucket from City Mill, so you can use it as a reservoir instead of the 10-liter bag. The filter will remove 99.999 percent of bacteria (including Leptospira).

Biggers also liked products such as Lifestraw Mission ($137.64) for families and large groups and Lifestraw Family ($62), also for households. The Sawyer Mini ($17.61), with a squeeze bag, works well for individuals.

We also were impressed with “Big Berkey,” a 2.25-gallon filtration system from New Millennium Concepts. At $260 it was the most expensive option but the simplest for families or large groups. (Berkey products range in price from $175 to $325.)

Resembling an old-fashioned office coffee machine, it has a shiny stainless-steel surface and a spigot on the bottom. Don’t let the retro look fool you; it is incredibly effective at eliminating everything from pathogenic bacteria to pesticides and heavy metals. We were able to assemble it like an erector set in less than 20 minutes.

The main task is to prime the heavy-duty filters, which involves a visit to the water faucet at the kitchen sink. The priming technique is a bit difficult to follow in the documentation, but if you watch the procedure on their videos, you realize it’s not difficult at all. (Their technical support, should you have questions, is first-rate.)

Continuing with the coffee maker analogy, once you’ve set up the Big Berkey, simply take off the lid and pour water into the upper chamber. Once the water filters through, tilt the spigot and out comes pure H2O. This product will even turn swamp water from Lake Wilson into something you can mix with baby formula.

This system is so efficient that the company suggests you test it by adding red dye to your water. (We tried it, and it filtered out the color.) The other cool thing about this product is that you don’t have to wait for the apocalypse to use it. Just put it on the kitchen counter and you’ll never have to buy bottled water again.

When the apocalypse comes you can be confident that with any of these systems, you and your family will have potable water, literally on tap.

Mike Meyer, formerly internet general manager at Oceanic Time Warner Cable, is now chief information officer at Honolulu Community College. Reach him at mmeyer@hawaii.edu.