What Kind of Water Is Safe to Use in an Aquarium?

Water comes from many sources and can be found in the most unexpected places. In October 2020, NASA astronomers announced they had detected the presence of H2O on the surface of the Moon. Even though this discovery was somewhat expected because of previous research, it’s very unlikely that lunar water would be safe for aquarium use. Water from the tap is what most aquarists choose for their tanks because it’s readily available and highly ideal once it goes through the dechlorination process. There are other water sources for fish keepers to consider, but they all have certain caveats. Let’s review what these sources have to offer.

Rain Water

You may think rain water is fine because this is how the ocean, rivers, creeks, lakes, and ponds get naturally replenished. The problem with rain water is that people fall short of replicating Mother Nature’s intricate processes. Unless you’re using a safe and efficient rainwater harvesting system complete with filtration and decontamination, you shouldn’t put precipitation in your tank. In the worst-case scenario, you could end up poisoning aquarium species with untreated acid rain.

Saltwater from the Ocean

In the case of reef tanks, you should theoretically be able to use water collected from the ocean, but only if you can go far enough offshore to avoid pollution. For example, if you live in South Florida, you wouldn’t want to collect saltwater from Biscayne Bay because it’s highly contaminated with everything from fuel to farming runoff. Here in San Diego, we’re lucky enough to have access to Scripps Pier in La Jolla. This water is pulled from the ocean in depths good enough to be very clean from pollutants, but the massive sand filters the water runs through to keep large partials out are harboring all kinds of creepy crawlies! This water is okay for fish-only tanks but not recommended for reef tanks.

Freshwater from Streams and Lakes

Before you collect water from a nearby creek, think about the aforementioned Biscayne Bay pollution scenario, which in many cases can apply to lakes and streams. You’ll first need to ensure you’re not collecting brackish water, which means you’ll have to test for salinity, minerals, and pH. If you live in an agricultural region, there’s a good chance irrigation runoff is polluting local water sources, and this means pesticides along with petroleum-based fertilizers.

Reverse Osmosis Water

Your local aquarium supplier may have this deionized water for sale like we have at Aquatic Warehouse. Reverse osmosis H2O by itself isn’t recommended for freshwater tanks because it lacks minerals, unless you add a supplement like Equilibrium or RO Right. However, it’s a good starting point for reef tank newcomers who wish to learn how to treat and condition water. After treated tap water, deionized H2O is the next best source, particularly if you’re contemplating a reverse osmosis filter and aeration system for your tank. Keep in mind that “pure water” isn’t ideal for an aquarium. It still needs to go through the nitrogen cycle and bacterial bloom processes before stocking the tank with hardy starter species.

In addition to making sure your water is safe for your fish to live in, you also need to have all of the essential supplies on hand to keep your tank running smoothly. Whether you need aquarium controllers or monitors, protein skimmers, beneficial bacteria, nutritious fish food, or any other aquarium supply, Aquatic Warehouse has it all. Stop by our store in Kearny Mesa, check out the selection on our website, or give us a call today at 858-467-9297 if you have any questions.