When it comes to maintaining a healthy backyard pond, topping up isn’t just about adding water. It’s about understanding water chemistry, evaporation, heavy rain events, and how all of these affect your fish and plants.
I’m Kev, and my goal is to help people build and maintain ponds without spending a fortune. If that sounds like your kind of thing, have a look around— there’s plenty here to get you started.
My Favourite Way to Top Up a Pond
Hands down, the best way to top up your pond is with rainwater. I’ve got a few tanks around the place, and it’s about as close as I can get to pure water without paying for it. It’s free, natural, and makes sense.
On my largest pond, I’ve even hooked up the gutters so when it rains, it tops itself up. It’s one of the simplest pond “automations” you can do.
Evaporation and Water Chemistry
Here’s the catch: when water evaporates, only the H₂O leaves. Minerals, salts, and nutrients stay behind.
Over time, as you replace water lost to evaporation, these materials build up. Some dissolve in the water, while others settle at the bottom or get caught in your filters.
If you’ve ever kept aquariums, you’ll know about water changes to dilute nitrates. It’s the same principle in a backyard pond. (Here’s my article on evaporation if you’d like to dive deeper →)
The Role of Your Biological Filter
Your pond’s biological filter is home to beneficial bacteria that power the nitrogen cycle — breaking down ammonia into nitrites and then nitrates. But it’s not just nitrogen you need to think about.
Phosphates can build up too, and algae absolutely love them. Some tap water even has phosphate added to protect pipes, which isn’t ideal if you’re trying to keep your pond clear. Bore water or untreated groundwater can also bring in extra salts and nutrients.
And here’s the kicker: even regular tap water isn’t consistent. Its chemistry can vary from suburb to suburb.
If you want to see what I add to my ponds to help boosts bacteria, treat tap water and phosphates- click here.
Topping Up with Tap Water
If you’re only adding a small amount of tap water, it’s usually fine. But for large top-ups or full refills, chlorine and chloramine can be a big problem. These chemicals can wipe out your biological filter in one hit.
For big refills, make sure you dechlorinate, or let the water sit for a while before adding it back into the pond.
Why Minerals Aren’t Always Bad
Not all minerals are the enemy. Some salts and minerals actually stabilise water chemistry, improve buffering capacity, and keep your pH steady. Serious fish keepers often monitor pH, kH, gH, nitrates and more.
Me? I prefer to let nature do the heavy lifting. With the right mix of rock, gravel, plants, and timber, you can build a pond that looks after itself. That’s exactly the idea behind my Pond Formulas Blueprint, which shows you how to create a stable, low-maintenance ecosystem.
What About Heavy Rain and Overflows?
On the flip side, what happens when you get too much water? A big storm can overflow your pond, flushing out the nutrients and minerals you’ve built up.
That might sound like a good thing, but sudden chemistry shifts can stress your fish. Natural materials like rock, gravel, plants, and wood help buffer these changes far better than a bare liner ever could.
And yes — fish escaping is a real risk during heavy rain. Below is a video → showing how I install them in some ponds. Whether you need one depends on your setup, your fish, and how much risk you’re comfortable with.
A Note on Native Fish
These days, I keep more and more native fish in my ponds. They’re naturally suited to local conditions, and if one does escape into a waterway, it’s less of a problem.
I’m not here to judge what’s ethical for you, but it’s worth thinking about. At the end of the day, water always finds a way.
Wrapping It Up
Topping up your pond isn’t just about adding water. It’s about understanding what’s in that water, how it changes over time, and how to design a system that works with nature instead of fighting it.
If you’d like to go deeper into building a pond that stays crystal clear and low-maintenance, check out the Pond Formulas Blueprint and have a look at the success stories from pond owners who’ve used it →.
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