The first step in calculating how much the water is going to cost for your aquarium is to find out how the local water company bills you. There are different ways that municipalities will bill for water. Some charge a flat rate, some are billed by volume or usage, some have pricing tiers. Once you have that information, it's pretty easy to just do the math.

The best way to do this is to find out how much you're paying per gallon of water.  If it's a flat rate, well your probably going to pay the same either way.  That said, with a tiered system it may benefit you to find out if water for the aquarium will bump you up into the next tier. 

How To Add Up Total Gallons Used Annually:

  1. Calculate how many gallons it takes to fill your aquarium x 1
  2. Calculate how many gallons you change out with your weekly water changes x 52
  3. Calculate how many gallons are used to replenish water lost to evaporation each week x 52
  4. Don't forget to account for the wastewater from your RO/DI system which can vary based on your particular RO/DI system. For every one gallon of product water, your RO/DI system will waste anywhere from 1 - 3 gallons of wastewater.

Once you have these numbers, add them all together to get your annual consumption of water in gallons. Multiply by your charge per gallon for a rough annual cost. Water costs can vary drastically depending on your location. If you have some sort of disposal or water treatment fees that are billed, you will want to add those into your final cost as well. 

**Pro-Tip - Purchase an RO/DI system to filter your tap water and produce 0 TDS RO/DI water for your aquarium. It will save you a considerable amount of money compared to buying filtered water at the local fish store. For most hobbyists, it pays for itself within the first 12 months of keeping your aquarium. A water saver RO/DI system that can produce a 1:1 product to wastewater ratio is especially useful in areas where water costs are higher or if you are charged some kind of processing/disposal fee based on usage. 

Example for 40-Gallon Aquarium

  1. 40 gallons
  2. Water Change of 5 gallons a week x 52 = 260 gallons
  3. Evaporating 4 gallons a week x 52 = 208 gallons
  4. RO/DI system with a 1:1 product to wastewater ratio = 580 gallons of wastewater

Add it all up and the total annual consumption of water for a 40-gallon tank is about 1,016 gallons of water. The average cost of water throughout the USA is about $1.50 - $3.00 per 1,000 gallons which means your tank will cost you no more than $3.00 annually for water alone.

Needless to say, the cost of water is typically not a significant ongoing expense. The initial investment in the tank and equipment will be the most costly. The ongoing costs in descending order: Fish food, additives, and filter media (consumables), the cost of energy, and finally water will make up the entirety of your expenses. 

Learn More With BRStv: What Is It Going To Cost? Setting Up A Saltwater Tank