View Full Version : Evaporation

DaKid Koi
07-24-2004, 05:59 AM
Ok Folks, here a question for all,
How much water evaporates from ur' pond on a Daily bases----- or a couple days-----or a week.
I know we all live in different parts of the USA or / and different parts of this world ,and we all have different types of weather, temperture, an so on, but on a base's overall.
I live in the north -east part of the US. Massachusetts that is, and I have been having to add at lease 1 to 2 inches of water to my pond evey 2-3 days. I figured my pond surface is about 196 sq. feet,which would come up to be 28' X 7' area. I figuring about 200 to 300 gallons ruffly every 3 days or so is being added. Plus I have running a 4 ' high water fall above the water surface also .
I know my weather here has been hot lately - 80- 85 and we have lots of humity in the air.

So my question is how much water do you all have to add on a daily-------- or a couple days-----or a week bases..
This is not including the 10 to 30 % water changes that we normally do or do you wait untill it needs water then do the water changes to it.

PS. I have check all areas of my pond for any links and I have not found any,so it's has to be just evaporation.

DaKid Koi :cool:

07-24-2004, 06:27 AM
Hi DaKid koi

Mine is around 180 square feet, and on average I lose around 1" in about 5 days. In th UK we do not have the same amount of sunshine as you, so that might explain the smaller loss.

07-24-2004, 06:30 AM
Good Question DaKid Koi, one that I will be keeping any eye the answers should make good reading.
The weather in England at the moment has not been very good :mad:and I think there has been more water going into the ponds than evapourating out :D
I'm in the middle of ponds so can't put an answer to your question but I know when it was really hot over here(god! I must have a good memory) that we had to top up on a weekly basis and I went down the same route as you thinking that I had got a leak.


07-24-2004, 06:31 AM
Hi merlin
Great minds think alike. :D

DaKid Koi
07-24-2004, 06:36 AM
Thanks merlin,
it was not to bad last year when the pond was only 2000 gal. and about 60 sq. feet , but this yr. I have notice a big different--- even my father-in-law keeps tell me boy you sure are adding a lot of water this yr. to the pond you sure you don't have any links .
If this keeps up I just may have to have the city water department hook up an out side meter to the house, for every gal. of water I paid for--- I pay :eek: double for the surage charge .

DaKid Koi :cool:

07-24-2004, 06:38 AM
Hi Jww

Well the Sun is actualy smiling on us this weekend, so expect huge losses :D.

07-24-2004, 07:23 AM
DaKid, I have been averaging an inch or so a day for the last couple of weeks. The pond is roughly 200 sq feet of surface (12x18), we have constant wind, spraybars run the length of the pond and the TT. So we go thru it every year but this year seems to be moreso for us as well. Luckily for us we do not have public sewage, we have out own septic system of DH would really be on my butt about it, the water bill aone gets me in enough trouble.

07-24-2004, 09:43 AM
It depends on how hot it is and how windy. A hot day with a nice breeze and the pond will drop an inch. A cloudy cool day and it won't drop at all.

Average is about 1.5 inches in a week.

Thomas T
07-24-2004, 10:22 AM
I live Houston and in the month of August - October, I lose around 1/4" of water per day. My pond is approx. 3000G and 200 sqft on water surafce area. The pond is in an open area & gets full sun most of the day with 5 mph wind over the surface. It also has a 3 ft. waterfall running at 3000G/hr & a 4 cuft TT running at 1000g/hr.

Thomas T
07-24-2004, 10:22 AM
I saved this information after reading about it in another newsgroup.


================================================== =====
Scientific calculation of Pond evaporation in Las Vegas
================================================== =====

note: some of the URL's may have changed....

Consider a 1/2 acre pond 8 foot deep... i.e. roughly 160' x 160' =
The total surface area of the water exposed to the air, A, is:

A = 25,600sqft

The volume is: 8'*25,600sqft = ~200,000 cuft.
and since water wieghs: 1 cuft/62lb

We have 200,000 * 62 = 12,400,000 lb of water.

The government and groups like ASHRAE have published monthly tables
with this kind of information in books and on the internet..

for Las Vegas, NV; go to:

and you will find that for July, the average high temperature is 106F
(but it gets to 110+ many times). The humidity ratio is: 0.0066 lb of
water/lb of air. From other sources, the average humidity is 12%RH

Recently, DOE did a study on POOL evaporation
(http://www.eren.doe.gov/rspec/Study1.htm), and concluded that Ashrae
was off a little bit.. anyways, here is there formula:

W = [(68.3+32*V)*(Pw-Pa)]/Y

W - evaporation rate, Lb/Hr-Ft.2
V - air velocity over water surface, MPH (in Las Vegas, V=7.0 mph)
Pw - saturation vapor pressure at the water temperature, inches of Hg
Pa - saturation vapor pressure at the air dewpoint, inches of Hg
Y - Latent heat at pool temperature, Btu/lb

First, let's find: Y

Using a Psychrometric chart, When the temperature is 100F outside and
the humidity might be about 12%. The sensible heat (at 100F dry bulb)
= 24 Btu/lb of dry air. WHile, at RH=12%, the Total heat = 30 Btu/lb;
thus, the latent heat would be: 30-26 = 4 Btu/lb

Y = 4 Btu/lb of air * [lb of air/0.0066 lb of water] = 600 Btu/lb of

Below, in an 'appendix', I show how I calculated Pw and Pa

W = [(68.3+32*V)*(Pw-Pa)]/Y

W = [(68.3+32*7)*(1-2)]/600 = -0.5 LB/hr-FT^2 are being evaporated
(The minus means that water is leaving the system...)

But remember, the total surface area of the water was:
A = 25,600sqft
W*A = 0.5 LB/hr-FT^2 * 25,600 FT^2
= 12,000 lb/hr * 1 hr/60 min = 200 lb/min * 1 gal/62 lb = 3

appendix: Pw and Pa calculations

There are tables which show the relationship between vapor pressure
and temperature. These tables form a logrithmic type curve. When you
take the natural logrithm of the vapor pressure (Vp), you get a
peicewise - linear formula in the form:
Vp(saturation) = exp[slope * Temp + 0.405] in millibars

For those of you which don't have tables, a rough equation is
available for temperatures between 20F and 115F.
Vp(saturation) = exp[(0.048-Temp/9500) * Temp + 0.405] in millibars

*IF* it's higher than 115F, the formula needs to be adjusted, for
instance, the (0.048-Temp/9500)
needs to equal the slope (column 4), so at 125F, the slope is: 0.036

To convert to inches of Hg (Mercury):
one millibar is equal to 0.02953 inches of mercury (Hg)

The column headings for the table below are:
Column 1 - Temp(degF)
Column 2 - Vp(saturated)
Column 3 - Ln(Vp)
Column 4 - slope
Column 5 - slope * Temp + .405
Column 6 - the calculated value for Vp(saturated)
0 1.50 0.405 0.046 0.405 1.50
5 1.90 0.642 0.046 0.635 1.89
10 2.40 0.875 0.046 0.865 2.38
15 3.00 1.1 0.046 1.095 2.99
20 3.70 1.308 0.046 1.325 3.76
25 4.60 1.526 0.046 1.555 4.74
30 5.60 1.722 0.046 1.785 5.96
35 6.90 1.931 0.044 1.945 6.99
40 8.40 2.128 0.044 2.165 8.71
45 10.20 2.322 0.042 2.295 9.92
50 12.30 2.51 0.042 2.505 12.24
55 14.81 2.695 0.042 2.715 15.10
60 17.71 2.874 0.042 2.925 18.63
65 20.99 3.044 0.042 3.135 22.99
70 25.00 3.219 0.04 3.205 24.66
75 29.61 3.388 0.04 3.405 30.11
80 34.99 3.555 0.039 3.525 33.95
85 41.02 3.714 0.039 3.72 41.26
90 48.09 3.873 0.039 3.915 50.15
95 56.20 4.029 0.038 4.015 55.42
100 65.63 4.184 0.038 4.205 67.02
105 76.17 4.333 0.037 4.29 72.97
110 87.79 4.475 0.037 4.475 87.79
115 101.4 4.619 0.036 4.545 94.16
120 116.8 4.76 0.036 4.725 112.73
125 134.3 4.9 0.036 4.905 134.96

Water is saturated vapor, and for a 80F water temperature:
Vp(saturated) = 25 millibar
Pw = 35 * 0.02953 =1.0 inches of Hg

For Las Vegas, Nevada, in July; the daytime temperature averages about
Pa = 65.6 * 0.02953 = 2.0 inches of Hg

DaKid Koi
07-24-2004, 10:43 AM
A BIG WOW Thomas T,
I guess you did some homework :)
Thanks alot I'm sure this will help others and my self about evaporation of pond water, Just another thing that Da NewB's should thing about befor getting in to this type of hobby if there thinking on going with BIG ponds and cost of water and like me where we also pay double for sewages to.

DaKid Kid :cool:

07-24-2004, 11:20 AM
There are a lot of factors to consider...

Do you have any type of water fall or spitter??? The evaporation from them will be greater when it is windy...

Also the surface area of your pond and what is around it...the more cement and rock the more evaporation...

Wind in general will play a big part in looking water to evaporation too...

It is windy here in S. Texas, as well as very hot!!! I loose about 4" ever 3 days in my little temp~pond.

07-24-2004, 11:34 AM
I have a leak. Both in my pond somewhere and in my water falls. Its kinda bad but we are not fixing it this year. We will fix it either in the fall or the spring. Right now I don't actually have to do any water changes but I still do.
My way of figuring evaporation is if I have to put the hose in the pond more then I have to put the hose in my pool its not evaporating its leaking :D
Simple but true. :cool:

07-24-2004, 12:48 PM
Hmmmm on average I notice about 1inch every 2-3days - hot days we can loose 1inch.

Thomas T, my head hurts but thanks for the informative post :D

DaKid Koi
07-25-2004, 06:59 PM
Thanks to all that reply to this thread
I hope this helps other's out of what they would expect when getting into the hobby that adding water due to evaporation will be a factor also not just the normal water changes.This is all an add cost to this hobby and to the health of our fine finned friends :)

Thanks again ,
DaKid Koi :cool:

Dorothy M
07-26-2004, 12:36 AM
We are around the corner from you here in Westport. We have about 400 feet of surface, two waterfalls and a stream. Like yourself, we add a few inches of water every day; more if it is hot, if it is windy, if the clamps let loose!

07-26-2004, 07:30 AM
My way of figuring evaporation is if I have to put the hose in the pond more then I have to put the hose in my pool its not evaporating its leaking :D
Simple but true. :cool:

My way of reckoning too... :D and as stated before...waterfalls and any types of water agitation will cause water to evaporate faster.

My problem seems to be the reverse this year...We have been getting sooo much rain, I've been having to pump the water out of both my pond and pool. :eek:


DaKid Koi
07-27-2004, 09:09 PM
Well still no change --every 2 or 3 day adding water to the pond -NOW it's time for me to get the out side meter install ,living in the city where I have to pay for water and surrage , not water bill getting a little crazy since I enlarged the pond more water changes-more evaporation, means more money :eek: :eek: HAHAHAHAHAHAHAH :rolleyes: Ok I'm better now :p , outside water meter will be install very shortly folks .

DaKid Koi :cool:

07-27-2004, 09:42 PM
Are you sure you don't have a leak???

Sorry making people paranoid is a hobby with me. :eek:

DaKid Koi
07-27-2004, 10:11 PM
No I shut down the waterfall and the veggie filter and all the air stones and venturis a while back (may 2 or 3 weeks ago)fill the pond to the top lasted about 4 days when down about 1/2 in.
the water in the veggie stream stood about the same water height ..
the waterfall barrel ...same thing...
check the overlap in the liner in the stream everything good there to...
I even shut down the filter pit and settlement tank which is made out of concrete and seal with water proof paint (3 coats) water stood the same ...
That when I ask the question about evaporation , everybody seem to have about the same evaporation as me with about the same surface area ,

So My conclusion has to be evaporation , my yard and pond is away in a direct windy area, I have a 4 foot high water fall 4 air stones going in the pond and 2 venturis .
With my 2000 gal pond last yr. I did not notice it as much do to it was only about 80 sq. ft. of surface area now it's much larger surface area around 200 sq. ft.
I have not measure the amount of water going into the pond when refilling /topping it---- but thats next to see exactly how much water i'm adding every fews days or so,tomorrow I check it when refilling it .

DaKid Koi :cool:

07-28-2004, 09:28 AM
OK, as long as you've checked for leaks. Seems you've done a thorough job of it. With that much air and waterfall I would think you would lose a significant amount to evaporation.

07-28-2004, 09:41 AM
I would still check your waterfall out real good....usually most leaks/water loss is from waterfalls.


07-28-2004, 09:44 AM
I was thinking that there might be some wicking some place near the falls...http://img.photobucket.com/albums/v194/crichardson/Smilies/4_12_6.gif