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Andy PhD DABT, Toxicologist
Category: Health
Satisfied Customers: 137
Experience:  Board certified with 20 years in research or consulting
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I had a few questions regarding dead bodies and water, so here

Customer Question

I had a few questions regarding dead bodies and water, so here goes,

How long must a body be submerged in water, both fresh water and sea water, to stop hypostasis/post mortem lividity from forming?

Also how much water would it take to float a person, i do not mean so you can see them on the surface but just keep them off the ground so the body is in the middle of the ground and surface, touching neither of them?
Submitted: 3 years ago.
Category: Health
Expert:  Andy PhD DABT replied 3 years ago.

I can help you with your questions. Submerging a body in water does not stop lividity. Lividity is caused by the blood no longer being pumped by the heart and instead of being dispersed through out the body, it settles in the lowest parts of the body by gravity. The blood stays within the blood vessels and so the lowest part of the body does not mean there is only one part of the body that is lower and so that is where all the blood will go, it means that there will be many low part of the body that blood will collect depending on the position of the body. After about 18 hours or so, the lividity will become fixed in place and will not move within the body if the body is turned. Until the lividity becomes fixed it will move in the body as the body is turned and the blood moves to the new lowest position. What that means is if, a person dies while on their back, lividity will start to develop in 2 hours into their back, but if the body is turned to laying on their stomach (anterior side) after 3 hours, then the lividity will shift and pool on their anterior. After 18 hours the lividity will not change positions if the body is turned. Submerging a person in water will not affect this, gravity will still act on the blood in the body and have it settle into the lowest spots. However, if a body is freely floating in water, then it will likely turn and be moved around so that lividity does not form normally since the lowest parts of the body keep changing. However, parts of the body that tend to sink the most, i.e. the feet and hands would likely still show lividity.

Your second question is about buoyancy. A body will float in water when it is alive because it weights slightly less per given volume compared to water, i.e. the body is less dense than water. If the water is salt water, which has a higher density, the difference in density of the body to the water will be greater and the body will float better. So what determines if something floats or sinks is density (how much a given volume weights, e.g. kg/L), it does not matter how much water the body is in as long as it is enough to cover the entire volume of the body. If the body is laying down, this could be as little as 25 cm deep. Now people are mostly water, but also contain some heavier elements, so if you cut an arm off and stick it in a tub of water it will sink because the density of the arm (tissue) is higher than water. However, when you consider the entire body, it has a lower density than water because the lungs are filled with air, which weights much less than water and takes up volume. So if you breath in and hold your breath you will float. If you breath out and have no air left in your lungs you will start to sink, though it is not possible to blow out all of the air in your lungs. If a dead body is in water, then the air will come out of the lungs and be replaced by the heavier water.

It seems that you have something in mind that you are thinking about, but are not asking your questions correctly. If you could tell me more about what you are asking and put your questions in context, then I could give you better answers.

Take care,
Customer: replied 3 years ago.

Hi, thank you for your reply, I would like to put across some more points im hoping you can clarify so I am totally satisfied I have covered all possible areas of the question.


1. In a more specific light a 28 year old Female is deceased and in a river of running water.


a) Does them being fully submerged in running water stop hypostasis/post mortem lividity from forming?

b) If so how long does it take to stop it from forming?

c) If it does not form why is this?

d) If it had already formed is there any way to reverse it in water?


2. If you could also answer the questions above but in a different scenario, say the river only has 3-5 inches of water in it, therefore the body would not be submerged completely as there is not enough water, however the water is still running.


I hope you can help me with these.

Many Thanks







Expert:  Andy PhD DABT replied 3 years ago.

Here are my responses:

No, being submerged in running water will not stop lividity from forming. Lividity will occur to some degree within 2 hours and be set within 18 or more hours. If the body is floating or free to move in the current, the constant motion of the body will reduce lividity in that settling of blood in many parts of the body will be minimal, but parts of the body that would consistently be positioned below other parts of the body, such as hands and feet, which are more likely to sink, would likely still have lividity. The cooler temperatures of the water may delay lividity becoming fixed into position. If the body is submerged in running water, but is held still, by sinking to the bottom or getting tangled on objects in the water, then lividity would not be hindered by continual body movement and would be noticeable.

Water absorbing into the body would not stop lividity because it occurs in about 2 hours and in that amount of time the body would still resist water absorption fairly well. Water would more rapidly absorb into the body through the lungs, eyes, mouth, anus, and vagina. However without the blood pumping, water would absorb by diffusion, which is a slow process and would not affect most of the body in that short amount of time.

Water does not stop lividity.

Water does not stop lividity.

After some time (days), water would absorb into the entire body and decomposition would help speed this process as the body's integrity and protection from water absorption would decrease. As the body decomposes and water absorbs the red blood cells would break open and degrade, so lividity may become less noticeable over time as decomposition occurs and the body absorbs water. When the red blood cells break open, the hemoglobin, which gives the red color of lividity would be able to diffuse out of the body over time as well as get broken down to chemicals that don’t have the red color. The diffusion of hemoglobin out of the body would occur more rapidly in the skin, so externally lividity may be less noticeable, however, lividity also occurs within internal organs, such as the liver, heart, etc... So the internal organs would be less exposed to the water and so less hemoglobin would diffuse out compared to the skin. A body may seem to have no lividity when viewed externally, but when autopsied lividity might be observed in the internal organs. Aquatic life also may feed on the body removing the outer tissues and making lividity less noticeable when viewed externally. Aquatic life feeding on the body also would assist in the water washing out blood or hemoglobin from the exposed tissue.

So over time, the decomposition and the flowing water would remove the lividity and this would be most noticeable externally, with lividity remaining longer in internal organs.

This is a simper situation because there is not enough water to flip the body over or allow it to move much. This would make lividity more pronounced than in the above scenario. All the other factors would be the same. Since the body is not fully submerged, aquatic life would not have as much access to the top part of the body which would not have lividity, so the parts of the body that would have lividity are in the water and accessible to aquatic life.

So if you see a dead body in the water and there is little or no lividity that you can see externally, then that is likely because the body was either moved around a lot before the lividity became fixed (in the first 18 hours or so after death) or that the body had started to decompose or has been eaten by aquatic life. For the former cause, it might be seen in body parts that remained consistently low in how the body was positioned. In the latter case, the internal organs might still show lividity.

I hope this helps answer your question. If you have questions about a specific case I would be glad to review the case for you and look over any reports you have. If you have reports (autopsy, toxicology, or police reports) I have had success before with having people upload files to (for free, you just have to register) so that I can view them.

Take care,
Customer: replied 3 years ago.

Hi Andy,


thanks for your reply, I was curious if you had a more confidential way for us to talk as the information I would like to disclose is confidential and regarding a case, which has had a lot of fabricated and contaminated evidence, therefore hopefully you may be able to review some case files and give me your opinion on the situation.

Expert:  Andy PhD DABT replied 3 years ago.
Yes I understand, that would be nice, but it is a rule that JustAnswer has. Unfortunately, there isn't a more confidential way to talk and what ever is said here is open to the public for anyone to read. However, what I have done in the past about this is have customers make a copy of their files and black out any personal information, like names and addresses, then have them scan those documents into Mediafire. They then copy and paste a link to that file in this JustAnswer website and send it to me. I get the file and download it, then tell you that I have the file and ask you to remove it from Mediafire right away, so at most the file is out there to be seen by others for about 24 hours (because of our time difference) and they have to use the link you send me to view the file, which limits the risk of anyone else downloading it. If all the personal information is blacked out then even if someone else gets it, it shouldn't reveal anyone's identity.

I understand your hesitation, so it is up to you if you feel comfortable doing that. If you want to tell me something in more confidence you could also type up what you want to tell me and put that file on Mediafire too. If you know of another website for uploading and downloading files you can use which ever you are most comfortable with. Mediafire is just the one I have used in the past and it is free.

Also, if you want my response to be more confidential, I can type it up and upload that to Mediafire for you to download as well. Then I remove my response when I know you have a copy of it, limiting how long it is open to the public.

So it is up to you, but I would be happy to look at any reports you may have about this case.

Take care,