Is Your Pond Leaking or is it Water Evaporation?

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Robert Pavlis

The biggest single fear of pond owners is that their pond starts to leak. Imagine removing all the rocks and much of the water to find the leak? It’s a lot of work.

You have noticed that the water level in your pond is dropping faster than before – or at least you think it is faster. Could it be a leak? Before you even start thinking about a leak, find out if it might just be normal evaporation. Doing this can save you both time and money.

What is a normal evaporation rate? That depends on many factors and nobody can give you an answer to this question, but it is easy to measure it yourself. I’ll show you how to do that in this blog post.

Is Your Pond Leaking or is it Water Evaporation?
Is Your Pond Leaking or is it Water Evaporation?

What Causes Water Evaporation in a Pond?

There are many factors that affect water evaporation in a pond.

  • Temperature
  • Wind
  • Humidity
  • Surface area of the pond
  • Water movement (waterfall or fountain)
  • Number of half submersed rocks
  • Amount of plants
  • Day length
  • Shading
  • Depth of pond

The same pond in Arizona can lose 5 inches a week, compared to 2 inches in New York. The rate of evaporation also changes with the seasons, being much higher in summer than in winter. Anything that moves the water (wind or fountain) will increase the rate of evaporation.

Compost Science for Gardeners by Robert Pavlis

A number of online sites says that the rate is about 1/4″ per day, but that is for a typical pond, in a typical location – whatever that means. It is much better to measure your own value.

Measuring Evaporation

This is a fairly easy process. Take a ruler or tape measure and measure the height of the water in a particular spot. It does not matter where you measure, but it is important that you measure in the same spot every time you take a reading.

If you have a flat overhanging edge like a flag stone or a dock, you can also measure the distance from the top of the flat object to the top of the water.

Wait a week and take another measurement. The change in height is the evaporation rate per week.

Do you have to wait a week? Not really, however it is a good idea to wait several days. The longer you wait, the higher the accuracy and the more you average out the variables, like a sunny day vs a cloudy day, and a windy day vs a calm day.

Measuring Water Evaporation on a New Pond

The best time to measure the water evaporation rate is just after finishing your pond. Provided you built it correctly, it won’t be leaking and so you know that any drop in the water line is due to evaporation. Take readings once a month for the fist season and store the values away for future use.

Then any time you suspect a leak, take another measurement and compare it to the saved values.

It would be great if everybody did this, but you are probably here reading this post because you suspect a leak in an existing pond and you didn’t measure evaporation when you first built it. I didn’t do it with my new pond either.

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Measuring Water Evaporation for an Older Pond

If you don’t have saved data you will have to take a different approach. Compare the evaporation rate in the pond with the evaporation rate in a container that does not have a hole in it. If they are the same, you don’t have a leak. If the rate is higher in the pond than the container, you have a leak.

Select a good container. Ideally it will be as wide as possible to more closely mimic the opening in your pond. A pail will work. A kiddy wading pool is excellent. A small jar is not very good.

The next step is to eliminate as many variables as possible. A pail sitting on the lawn has sun beating down on it, which heats the water more than the water in a pond. The pond is probably deeper than the pail, and deeper water is colder, which keeps the temperature at the surface cooler as well. A very tall pail would be great, but not very practical. One way to eliminate some of these variables is to set the pail in the pond, so the top rim is an inch or two above the water line. You can also dig a hole in your garden, and bury the pail up to the rim.

Fill the pail with water. This should be the same temperature as the pond water and using pond water would be great. Fill it almost to the rim, so that any wind will affect it just like the open pond.

Make sure the pail and the pond have similar shading. Turn off all pumps so that the moving water from pumps does not affect the drop in level.

Measure the water height in the pond and in the pail. Wait several days to a week and measure it again. If the pond has a leak, the water level in it will drop faster than in the pail.

Natural Pond With a Leak

If the above procedure shows that you have a leak in a natural pond without any pumps or water falls, the leak is in one of two places; in the pond itself, or around the edge of the pond. If you are using a proper rubber liner, it is quite rare to find a leak in the pond. It is almost always around the edge of the pond. Some rocks have moved, or soil has settled and now the liner is below the water line, and water seeps out. Even the loss of a small amount of water adds up quickly.

This video shows you a mistake I made in one of my ponds. I used soil in the pond and let it cover the edge of the pond. Even though this soil level was well above the water line it still sucked water out at quite a fast rate.

YouTube video

A Leak in a Pond With Pumps

Pumps and waterfalls add another level of complexity when looking for a leak. By turning the pumps off in the above procedure, you have eliminated the pumps and plumbing as a potential problem. If a leak is found it has to be in the pond and not in the waterfall or pump.

However, if you followed the above procedure and found no leak, it is still possible that your plumbing or the waterfall is leaking. But at least you know it is not the liner or the edge of the liner.

Turn the pump back on and remeasure the rate at which water drops. If you have more than one pumping device, turn them on one at a time so you can test each one separately. The thing to keep in mind is that a pump will cause more water movement in the pond than in the pail, so a greater drop in the pond compared to the pail is normal. How much of a difference is normal? That is hard to say since it depends on the amount of water you are moving, how much spray you get from a waterfall or fountain, how much of that spray lands outside of the pond, etc.

Moving water in a waterfall can cause a significant amount of evaporation.

Check all of the plumbing joints that are outside of the pond to make sure they are dry. Any leaking joints inside the pond will not contribute to a drop in water level.

If all of the joints are dry, the leak is almost certainly in the waterfall and can be due to a hole in the liner, a settling liner, rocks that have shifted, or cracks in a seal.

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Robert Pavlis

I have been gardening my whole life and have a science background. Besides writing and speaking about gardening, I own and operate a 6 acre private garden called Aspen Grove Gardens which now has over 3,000 perennials, grasses, shrubs and trees. Yes--I am a plantaholic!

4 thoughts on “Is Your Pond Leaking or is it Water Evaporation?”

  1. Interesting and informative pond repair blog. It caught my interest when it talked about the pond leakage point. Well, after finding the leak, all you need to do is seal or repair it on a priority basis. I’d like to recommend a pond liner that is also used for its flexibility and durability with multiple pond materials including existing EPDM membranes, concrete, acrylics, fiberglass, etc. Pond Pro 2000 is a butyl liquid rubber liner that can be easily applied to all types of surfaces and can last three times longer than other acrylic pond liners. Its only one-coat application can seal the surface for many decades, and in case of leakage or accidental damage, repairing and recoating it is very easy.

  2. I lose 3-4 inches every 12 hrs on my stream and there are no leaks and my side edges are high so nothing is overflowing or splashing out. But there is some rocks that do get lightly splashed, can that be the issue?

  3. I am digging a pond next week, about a 1/3 acre. I am in solid clay, but am nervous it won’t hold water..i will be filling it with a well. Have you heard of many people having success with a clay pond? Appreciate your feedback


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