Introduction
I am doing home automation. I have learned how to use a relay, then a solenoid. Now I am starting a new thing - Solenoid Valve.
I have already bought a couple of solenoid valves for my hobbyist projects. But I don't know how to use them. So as usual, first thing first is to google SparkFun. I read the description but found too many jargons I don't understand. They say I also need to use a pump. I bought a couple of pumps but do not know if they are useful (What the hell is GPH350?), ...
Anyway, I read AquaTech's datasheet and have learned more. But SparkFun smallest valve is 3/4 in (and their big mac's smallest soda is a whopping 12oz!), too large for my small cat. So I looked for smaller valves , ...
I visited Adafruit and found smaller, 1/2" valves, with a very newbie friendly user guide. So I forgot SparkFun and followed Lada Ada!

But I always find Adafruit's toys too expensive. So I searched TaoBao and found their cheapest goody, only 8 yuans:
Puro-XD-12 12V 1/4" Solenoid Valve Quick Connect ¥8 (7 times cheaper than SparkFun!)
Update 2019jan19hkt1315
I have shortened the topic title. My way is to make the title as short as possible, but not shorter. My answer also as short as possible, but as long as required, ...

My Way - Frank Sinatra 74,771,293 views
https://www.youtube.com/watch?v=6E2hYDIFDIU
Appendices
SparkFun 12V 3/4" Solenoid Valve $8
https://www.sparkfun.com/products/10456
Description
Have you ever wanted to control the flow of a liquid using your computer or microcontroller, but didn’t know how? Well, here’s how: The 12V solenoid controlled fluid valve. Simply connect a fluid source to the ¾" threaded inlet and it will interrupt the flow until 12V is applied to the fast-on connectors on the solenoid.
Note: This is not a gravity-feed solenoid. This means that you will need enough water pressure to fully open the valve. Check the datasheet below for exact details. It operates at a minimum of around 3 PSI, allowing around 3 L/min of flow. Although the datasheet shows the valve working at 220 VAC, it’s actually 12 VDC. Our 350 GPH pump does not have enough pressure for this valve. A garden hose or other pressurized system should work just fine.
Aqua Tech AQT15SL 1/2" BSP inlet and 12mm outlet
https://www.sparkfun.com/datasheets/Rob ... Valves.pdf
Adafruit Plastic Water Solenoid Valve - 12V - 1/2" $7
https://www.adafruit.com/product/997
Description
Control the flow of fluid using the flow of electrons! This liquid valve would make a great addition to your robotic gardening project. There are two 1/2" (Nominal non-taped National Pipe) outlets. Normally, the valve is closed. When 12VDC is applied to the two terminals, the valve opens and water can push through. The valve has a gasket arrangement inside, so there is a minimum pressure requirement of 0.02 Mpa (3 PSI). Also, liquid can only flow one direction.
We tried this solenoid at various DC voltages and found we could actuate it down at 6VDC (although it was a little slower to open). Here is the current draw table for various voltages. We suggest a TIP120 or N-Channel power FET with a 1N4001 kickback diode to drive this from a microcontroller pin. For a power supply, our 9V 1A or 12V 1A power adapters will do the job.
If you want a beefier water valve, we also carry a brass version which does not have a minimum pressure requirement and can be used with liquid flow in either direction.
Voltage/Current
6V160 mA
7V190 mA
8V220 mA
9V240 mA
10V270 mA
11V300 mA
12V320 mA
These solenoids are not rated for food safety or use with anything but water.
Tchnical Details
1/2" Nominal NPS
Working Pressure: 0.02 Mpa - 0.8 Mpa
Working Temperature: 1 ℃ - 75 ℃
Response time (open): ≤ 0.15 sec
Response time (close): ≤ 0.3 sec
Actuating voltage: 12VDC (but we found it would work down to 6V)
Actuating life: ≥ 50 million cycles
Weight: 4.3 oz
Dimensions: 3.3" x 1.69" x 2.24"
TaoBao Puro-XD-12 12V 1/4" Solenoid Valve Quick Connect ¥8
https://item.taobao.com/item.htm?spm=a1 ... 0735960072