well you could in theory avoid a meter, you would need to do some fairly complex, but also fairly well documented calculations, these being based on the simple rules of thermodynamics Energy (in) = Energy (out), using base Si unit conversion, taking in to account total absorbed radiation (in) being equal to the rate of transpiration + Conduction and Convection + Photosynthesis +(-Respiration) + G (where G is Storage - eg a leaf)
You can make some basic inputs based on your light watts, msq growing area, and use a base photosynthetic efficiency of about 2% (even this is probably generous where we use a 1000W/m2 in a 0.04% CO2 environment :), but it will give you some input figures from which to base the water loss calculation.
Essentially you are determining environmental balance, eg how much water does a plant lose over a 24hour period and therefore, how much do we need to replace.
I have hugely simplified this so i dont write an essay as usual, its not just as simple as knowing your light watts, you need to know the total energy absorbed, which includes understanding that being, reflected, transmitted, ommitted etc and this isnt just your shortwave energy, this is long wave too, eg surface temps.
The thing to remember, plants must breathe a gas which exists in concentrations approximately @ 0.04%, this means they must leave stomata open to breathe in order to get enough air for the day, and as a consequence they loose lots of water based on certain conditions,, but it is possible to know just how much if you are prepared for the work to calculate. There are many resources to help explain how laws and maths apply to this, there are many charts and pre calculated materials in databases, eg those covering ALBEDO, Plancks Equation, Stefan Boltzman Law and so on, necessary to complete the process.
I can teach you but you would have to pay me LOL :)