Answer:
The answers are:
- haya
- hagamos
- ahorremos
Step-by-step explanation:
- Tendremos que conservar agua aunque haya suficiente. (Subjunctive)
- Las especies en peligro de extinción normalmente mejoran sus números tan pronto como nosotros hagamos algo para protegerlas. (Subjunctive)
- A menos que ahorremos agua, tendremos problemas de sequía. (Subjunctive)
As you may know, the subjunctive mood is to talk about things that are possible but not certain, whereas the indicative mood is the opposite (certainity). Thus, the three sentences are subjunctive as they express desire and possiblity, but it's not a fact, as not all of us will save water or do something to protect the danger species.
On the other hand, "haya" is the present for of "haber" for talking about something, in this case "agua" "Hagamos" is -we do-, as it is indeed talking about "nosotros"- we. And finally, same happens with number three, talking about us.