1) You don't need to pump water to keep your plants alive. You may think they're dying because you can't access them through the workshop and they don't say harvest, but, give it a day or so, they'll be back! If they're dead, especially through an attack, they'll say repair (which doesn't make any sense to me, but, hey, whatcha gonna do). That has been my experience. That's probably why you don't assign settlers to do it. My pumps are always over by the bathrooms. Makes more sense to me.
2) My trick with guard towers is to place them with walls on either side and then use the high platform to put a gun on one or both sides of it. I mean, after all, you're guards need to use the guard tower. Can you imagine the lack of room!
Now that my internet is finally back on I'm going to start posting settlement pics and videos for people to see. I don't experience nearly as many issues as, apparently, others do with attacks and destruction so, apparently I'm doing something right.
Tip from me though: Be sure your defense is equal to or greater than your water + your food and you'll be fine. Also: Arm your guards well! I don't find that armor does all that much good (thus the men are in harnesses and the women in Road Leathers), but, if you arm them well, most threats are not that big a deal.
Oh! And learn where your spawn points are. That's one of the reasons why, I'll use Sanctuary as an example, I only build in a certain area and put up walls and gates with funneling points. There are 4 that I've discovered at Sanctuary although I suspect there's a 5th somewhere that I haven't discovered yet. Even SuperMutants and Deathclaws can be funneled. With the right combo of turrets and defenders, they don't stand a chance.