Hi im pretty sure this might be impossible but im looking to sense a water flow averaging at 400ml/min but will probably want to go lower 100 or 200ml/min and hopefully less than 300$ but it seems theres pretty much nothing that can do is this possible? If so how?/with what? Thanks
Should also mention its ethanol and water so the density will vary slighty
Count the drops like they do with IV bags.
Have you tried a rain gauge?
Ethanol and water ? that is harder than dry gas.
What is your project ?
Some people want to use a pump with a valve and a flow meter to measure the amount of liquid that will be added to something else. For something like that, a peristaltic pump or a dosing pump can do the same.
For dry gas: go to mouser.com and you can find them. Sensirion seems to have nice flow sensors. Omron is cheaper. The Omron D6F series have a 100ml/min sensor: D6F-P0001A1. That one can easily be connected to a 5V Arduino board.
For liquid under 1000 dollars, the Sensirion LG01-2000A005 shows up at mouser.com. That is not a sensor, only a switch that detects flow 
The IDT FS2012-1001-LQ is for liquid and gas and is 500ml/min. However, they call it a liquid level sensor. Very confusing.
Outside mouser.com are more special sensors. Some are with a "microturbine", but often 1000 dollars or more.
Sorry, I could not find the perfect sensor yet.
mikb55:
Count the drops like they do with IV bags.
https://www.youtube.com/watch?v=RY53ubSX6ng
there is still a low stream flowing so I think counting individual drips won't work but I'll look into it.
Koepel:
Ethanol and water ? that is harder than dry gas.
What is your project ?Some people want to use a pump with a valve and a flow meter to measure the amount of liquid that will be added to something else. For something like that, a peristaltic pump or a dosing pump can do the same.
For dry gas: go to mouser.com and you can find them. Sensirion seems to have nice flow sensors. Omron is cheaper. The Omron D6F series have a 100ml/min sensor: D6F-P0001A1. That one can easily be connected to a 5V Arduino board.
For liquid under 1000 dollars, the Sensirion LG01-2000A005 shows up at mouser.com. That is not a sensor, only a switch that detects flow
The IDT FS2012-1001-LQ is for liquid and gas and is 500ml/min. However, they call it a liquid level sensor. Very confusing.
Outside mouser.com are more special sensors. Some are with a "microturbine", but often 1000 dollars or more.
Sorry, I could not find the perfect sensor yet.
That sensirion sensor seems very good but it might be slightly too low although I could have another use. I know its hard to find fluid sensors at flow rates that are low and not thousands of dollars I did find this however
http://uk.farnell.com/cynergy3/uf08b100/flowmeter-ultrasonic-0-8l-min/dp/1877555?MER=mktBestSellerB
Although I am skeptical of the accuracy at the low end of the flow rates, although I can deal with large inaccuracies. It says 95% accurate but I don't know if that is even at lower limits But yes its difficult.
It's minimal flow rate is 100 ml/min. It might be inaccurate below 100 ml/min or it might not work at all below 100 ml/min. You could ask the manufacturer about its behaviour. Perhaps it is possible to make a curve or table in software for a specific sensor to compensate the inaccuracy.