Many argue that we should not drink almond milk as it uses scarce water. (e.g. https://www.ethicalconsumer.org/food-drink/shopping-guide/soya-non-dairy-milk). However given that consuming almond milk helps finance removing carbon from the atmosphere, would it not be defensible to consume it? For example in California, the water shortage does not drive species into extinction not does it deprive people of necessary access to clean water. But it could mean less industrial animal husbandry and less area of green lawns. I think less water to such purposes is no problem and means we probably should step up consumption of almond milk, especially in areas where water shortage is more of a nuisance and not an ecological or social issue.
The issue is really with sustainability rather than scarcity, and it is also linked to ecological issues. An article in the Berkley University web site gives some background information. In order to maintain their farms through long droughts the farmers want more rivers dammed. Damming a river means flooding an ecologically rich valley. There might be potential for a beneficial impact on the carbon budget, but the creation of a new artificial reservoir also has the potential for a very damaging impact on global methane emissions (a side effect of drowning the valuable biosphere in the river valley).
A report from the Pacific Institute describes the ecological damage associated with reduced flows of fresh water into the Sacramento Bay caused by unsustainable extraction of water for agriculture (as an example .. this is not an exhaustive study of damage caused). The water shortage is threatening a rich ecosystem in the delta, which also has potential economic impact because it is a an important home for wild salmon.
The Pacific Institute report also suggests that current agricultural output could be produced with less water (or more efficient use of existing water through better management), so it may be possible to get the almond milk in a sustainable way, but there does appear to be a need (or at least a valid case) to exert some consumer pressure to reduce the level ecological damage caused by existing levels of water use.
Quick answer, from best to worst, in terms of water only:
- Good: Oat milk, soy milk
- Okay: Almond milk
- Worst: Dairy milk
There are a lot of "news" articles about the water and carbon impacts of milk. I cannot find the one I just read, but I've included a few below as a reference. Some of it depends on where things are grown, and how a rise in one type displaces another. Water and carbon evaluations need to be measured from the food sources and land displacement, so it is a little tricky. That being said, there are some rough generalisations that seem to simplify this decision for most of us in our daily lives.
This finding surprised me a little but dairy milk is the worst for water. It's also the worst for GHGs, which is less surprising.
Almond milk was reported as being better than dairy milk for both, but it is still worse for water than all of the other milk sources. Plus almonds are displacing other crops in California, which is bad. Apparently there's a good return on almond crops, but only because they're not paying for the water, the cost of which is kept relatively low so that it doesn't stunt all farming in general. It's like fuel costs, it needs to go up in price to change use, but has huge impacts everywhere if it does.
Soy and oat milk are both good for water and GHGs (relative to the other options) and, depending on where you live, have a good chance of being grown locally (vs. say coconut milk). That helps on GHGs, but obviously cannot be applied equally to everyone. If you are in the US or Canada, there's a good chance it's being sourced locally.
Note that if you're switching from dairy milk you will need to up your protein from other sources. Soy has about 2/3rds the protein of dairy, and oat about 1/2 the protein of dairy. You also have to watch for sweetened alternative milks, as if we're not getting enough sugar as it is.
My favourite for cereals is soy milk as it has a wheatier taste, which goes great with grains. I've generally found all of the other alternatives (other than soy) a little thin and watery. They're not unbearably so and you get used to it, but it's an adjustment. They're more like (dairy) skim milk.
A bonus for these milk alternatives is that they don't curdle. I often cut up fruit in my cereal, and if left too long it would curdle the dairy milk, especially if it was acidic. I've heard all of these milk alternatives can be used for DIY yoghurt, which surprised me too.
Sadly soy milk is a high-FODMAP food in the US/Canada. Apparently the New Zealand/Australian production uses the whole bean and works out to be low-FODMAP. (Not than anyone asked. :)
Note that diary milk is rated worst when it's from big, industrial farms. Since they're the major source of milk (and beef, etc.), it is these sources that are usually evaluated and reported. When it is from small farm holdings the GHGs are apparently negligible. I presume it is because the waste is in proportion to what can re-used locally (e.g. tilled back into the soil) and there aren't giant piles of manure degrading anaerobically, producing lots of methane. I guess on small holdings, methane burps are relatively negligible. :) They still have sizable use requirements, however.
Also, if these cattle are used for meat (which, I know, has the same water and GHG issues), the water and GHG side effects of this dairy milk are similarly negligible.