How much water should I use when making this in the slow cooker? I imagine it would be fewer than 7 cups of water.

Keep in mind, too, that slow cookers vary, depending on size/diameter, age/"horsepower", etc. That said, this recipe is so forgiving. There is no single perfect dal texture or consistency. I don't use my slow cooker for dals, given how quickly red lentils cook up on the stove. Also, I'd want to see the original slow cooker recipe before converting Nicholas' recipe. I know that this recipe has tomatoes in it. Under no circumstances should you put raw onions in the slow cooker with tomatoes or any other high-acid ingredient. They simply must be sweated thoroughly at the outset or the outcome will be, in a word, awful. (This is one lesson you don't want to learn the hard way.) ;o)

And in the related article, Nicholas noted that the first time he made the recipe he did so in a slow cooker, so you could always send him a direct message to ask, just click the envelope button on his profile page here: http://food52.com/users/65584-nicholas.

The recipe that this was adapted from (in Anupy Singla's The Indian Slow Cooker) actually calls for 9 cups of water, and as Nicholas notes in the headnotes, when using a slow cooker, Singla recommends cooking the lentils on low for 5 1/2 hours and then for another 30 minutes after adding the coconut milk.