Water feature losing a lot of water in a short period of time - evaporation or leak?

Question

I have a 700-1000 gallon water feature (rough calculation) that seems to lose hundreds of gallons of water in sometimes just ~10 days. Essentially I can lose 1/3 of the water in the feature in just over a week.

• This is definitely more prevalent depending upon how high I have the water pressure and I've tracked some of this down to some spill over. I've lowered the pressure and that helps quite a bit.
• Some of this is definitely evaporation because it is much more severe in hot weather. We have rocks around the feature which bake in our 100 degree California sun, this may be part of it. During winter I don't have these problems nearly as much.
• I'm also concerned that I may also have a leak underground given the amount of water that can disappear. I've also heard from my next door neighbor that they see some damp areas on their side from time to time. It could be from our pond, but I am not sure.

My question is: Is it possible that evaporation is the main culprit here or is it likely that there is a leak?

Follow up question: Who would I contact to do a leak investigation? I've been trying to determine the best way to figure this out myself but if I do have a leak, that part may be over my head.

Update

To add clarity regarding the evaporation: We have rocks surrounding our pond that get water on them, the rocks heat up and certainly there is some amount of evaporation. I would think this would be the most prominent source of evaporation due to the heat that the rocks absorb from the sun, particularly around the area where the water comes out.

Answer 1

Check a meteorological station near you - most have a "pan evaporation rate" measurement which if your losses are similar will prove it is evaporation.

If they are different - except for your spill over then you have a leak.

Answer 2

Your picture is cut off. I see a tumble-down over a waterfall. I could see over-splash or the wind causing some losses. However, you said pressure is a factor in losses, and that wouldn't be the case for a simple waterfall. Pressure could only matter significantly if a non-pictured part of this was a fountain which sprays water into the air.

If you actually meant "flow" not "pressure", and you don't have any fountains, then it's due to more water cascading over the waterfalls.

Cooling ponds work exactly that way: they intentionally cause evaporation, which causes the latent heat of vaporization to steal heat out of the water which falls back down.

That, plus the large surface area and normal summer weather are sufficient to explain your water loss.

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The physics of it are this: Sunshine has 1000 watts per square metre, or 3400 BTU/hour. Around 320 BTU/hr per square foot square on to the sun.

When 1 pound of water vaporizes, it must absorb 970 BTU of energy simply to shift from liquid to gaseous water at the same temperature. 8.3 pounds per gallon (1 pound ~= 1 pint or 1/2 liter).

So if you have 1 square meter of square-on sunshine hitting the wetted area most of the day, given the generally terrible albedo (reflectivity) of most materials, you'll have north of 3000 BTU/hr to get rid of. That alone accounts for 3 pounds/pints (1.5kg/l) per hour of water loss. There's also some loss to atmosphere, since the atmosphere wants to equalize at a fairly high percent humidity. But this varies by temperature and ambient humidity (very bad in the desert, not so bad on a muggy day).

Answer 3

Inspection wells.

Dig a few narrow holes, install pipes in them. Then you can see the water level in different places.

At two properties, I used digging tools to dig half a metre down (18’’). I placed rags over the ends of pieces of pipe. Then I put the scrap PVC pipe in the holes and filled in outside the pipes. Also placed caps on the pipes to keep them clean. I can see water level anomalously high near the leaking area compared with further away.